Coagulation Harr

2.1 Coagulation and Fibrinolytic Systems/Reagents and Methods

Which of the following initiates in vivo coagulation by activation of factor VII?

A. Protein C

B. Tissue factor

C. Plasmin activator

D. Trombomodulin

B. Tissue factor

B In vivo, activation of coagulation occurs on the surface of activated platelets or cells that have tissue factor. Tissue factor is found on the surface of many cells outside the vascular system (extrinsic). Upon vascular injury, TF is exposed to the vascular system. TF has high affinity for factors VII and VIIa. TF activates factor VII to VIIa and forms TF-VIIa complex. TF-VIIa complex in the presence of Ca+2 and platelet phospholipid activates factors IX to IXa and X to Xa. Factor Xa forms a complex with cofactor Va (Xa-Va) on the surface of the activated platelets. Factor Xa-Va complex in the presence of Ca+2 and platelet phospholipid converts prothrombin (factor II) to thrombin (IIa). Thrombin acts on soluble plasma fibrinogen to form a fibrin clot, which is stabilized by activated factor XIII (XIIIa). In addition, activated factor IX (IXa) forms a complex with activated cofactor VIII (VIIIa) o

Which of the following clotting factors plays a role in clot formation in vitro, but not in vivo?in vitro clot formation and not in vivo coagulation?

A. VIIa

B. IIa

C. XIIa

D. Xa

C. XIIa

C Factor XIIa does not play a role in coagulation in vivo; however, in vitro, the deficiency of this factor causes a prolonged APTT result. In vitro, factor XII is activated by substances such as glass, Kaolin, and ellagic acid, and in vivo it may be activated by exposure to a negatively charged cell surface membrane such collagen as well as kallikrein (an activated form of prekallikrein) and high molecular weight kininogen (HMWK). In vivo, factor XIIa plays an important role in the fibrinolytic system by activating plasminogen to plasmin. Plasmin degrades the fibrin clot at the site of injury. Deficiency of factor XII is associated with thrombosis and not bleeding. Factors VIIa, Xa, and IIa play a role in vivo and in vitro.

The anticoagulant of choice for most routine coagulation studies is:

A. Sodium oxalate

B. Sodium citrate

C. Heparin

D. Ethylenediaminetetraacetic acid (EDTA)

B. Sodium citrate

B The anticoagulant of choice for most coagulation procedures is sodium citrate (3.2%). Because factors V and VIII are more labile in sodium oxalate, heparin neutralizes thrombin, and EDTA inhibits thrombin's action on fibrinogen, these anticoagulants are not used for routine coagulation studies.

Which ratio of anticoagulant-to-blood is correct for coagulation procedures?

A. 1:4

B. 1:5

C. 1:9

D. 1:10

C. 1:9

C The optimum ratio of anticoagulant to blood is one part anticoagulant to nine parts of blood. The anticoagulant supplied in this amount is sufficient to bind all the available calcium, thereby preventing

clotting.

Which results would be expected for the prothrombin time (PT) and activated partial thromboplastin time (APTT) in a patient with polycythemia?

A. Both prolonged

B. Both shortened

C. Normal PT, prolonged APTT

D. Both normal

A. Both prolonged

A The volume of blood in a polycythemic patient contains so little plasma that excess anticoagulant remains and is available to bind to reagent calcium, thereby resulting in prolongation of the PT and APTT. For more accurate results, the plasma:anticoagulant ratio can be modified by decreasing the amount of anticoagulant in the collection tube using the following formula: (0.00185)(V)(100-H) = C, where V = blood volume in mL; H = patient's Hct; and C = volume (mL) of anticoagulant. A new sample should be drawn to rerun the PT and APTT.

What reagents are used in the PT test?

A. Thromboplastin and sodium chloride

B. Thromboplastin and potassium chloride

C. Thromboplastin and calcium

D. Actin and calcium chloride

C. Thromboplastin and calcium

C Thromboplastin and calcium (combined into a single reagent) replace the tissue thromboplastin and calcium necessary in vivo to activate factor VII to factor VIIa. This ultimately generates thrombin from prothrombin via the coagulation cascade.

Which test would be abnormal in a patient with factor X deficiency?

A. PT only

B. APTT only

C. PT and APTT

D. Trombin time

C. PT and APTT

C Factor X is involved in the common pathway of the coagulation cascade; therefore, its deficiency prolongs both the PT and APTT. Activated factor X along with factor V in the presence of calcium and platelet factor III (PF3) converts prothrombin (factor II) to the active enzyme thrombin (factor IIa).

Which clotting factor is not measured by PT and APTT tests?

A. Factor VIII

B. Factor IX

C. Factor V

D. Factor XIII

D. Factor XIII

D Factor XIII is not measured by the PT or APTT. Factor XIII (fibrin stabilizing factor) is a transamidase. It creates covalent bonds between fibrin monomers formed during the coagulation process to produce a stable fibrin clot. In the absence of factor XIII, the hydrogen bonded fibrin polymers are soluble in 5M urea or in 1% monochloroacetic acid.

A modification of which procedure can be used to measure fibrinogen?

A. PT

B. APTT

C. Thrombin time

D. Fibrin degradation products

C. Thrombin time

C Fibrinogen can be quantitatively measured by a modification of the thrombin time by diluting the plasma, because the thrombin clotting time of diluted plasma is inversely proportional to the concentration of fibrinogen (principle of Clauss method).

Which of the following characterizes vitamin K?

A. It is required for biological activity of fibrinolysis

B. Its activity is enhanced by heparin therapy

C. It is required for carboxylation of glutamate residues of some coagulation factors

D. It is made by the endothelial cells

C. It is required for carboxylation of glutamate residues of some coagulation factors

C Vitamin K is necessary for activation of vitamin K dependent clotting factors (II, VII, IX, and X). This activation is accomplished by carboxylation of glutamic acid residues of the inactive clotting factors. The activity of vitamin K is not enhanced by heparin therapy. Vitamin K is present in a variety of foods and is also the only vitamin made by the organisms living in the intestine.

Which statement about the fibrinogen/fibrin degradation product test is correct?

A. It detects early degradation products (X and Y)

B. It is decreased in disseminated intravascular

coagulation (DIC)

C. It evaluates the coagulation system

D. It detects late degradation products (D and E)

D. It detects late degradation products (D and E)

D The fibrin degradation product (FDP) test detects the late degradation products (fragments D and E) and not the early ones (fragments X and Y).

Which of the following clotting factors are measured by the APTT test?

A. II, VII, IX, X

B. VII, X, V, II, I

C. XII, XI, IX, VIII, X, V, II, I

D. XII, VII, X, V, II, I

C. XII, XI, IX, VIII, X, V, II, I

C The APTT test evaluates the clotting factors in the intrinsic pathway (XII, XI, IX, and VIII) as well as the common pathway (X, V, II, and I).

Which coagulation test(s) would be abnormal in a vitamin K-deficient patient?

A. PT only

B. PT and APTT

C. Fibrinogen level

D. Thrombin time

B. PT and APTT

B Patients with vitamin K deficiency exhibit decreased production of functional prothrombin proteins (factors II, VII, IX, and X). Decreased levels of these factors prolong both the PT and APTT.

Which of the following is correct regarding the international normalized ratio (INR)?

A. It uses the International Sensitivity Ratio (ISR)

B. It standardizes PT results

C. It standardizes APTT results

D. It is used to monitor heparin therapy

B. It standardizes PT result

B INR is used to standardize PT results to adjust for the difference in thromboplastin reagents made by different manufacturers and used by various institutions. The INR calculation uses the International Sensitivity Index (ISI) value, and is used to monitor an oral anticoagulant such as warfarin. INR is not used to standardize APTT testing.

Which of the following is referred to as an endogenous activator of plasminogen?

A. Streptokinase

B. Transamidase

C. Tissue plasminogen activator

D. Tissue plasminogen activator inhibitor

C. Tissue plasminogen activator

C Tissue plasminogen activator (tPA) is an endogenous (produced in the body) activator of plasminogen. It is released from the endothelial cells by the action of protein C. It converts plasminogen to plasmin. Streptokinase is an exogenous (not made in the body) activator of plasminogen.

Which protein is the primary inhibitor of the fibrinolytic system?

A. Protein C

B. Protein S

C. α2-Antiplasmin

D. α2-Macroglobulin

C. α2-Antiplasmin

C α2-Antiplasmin is the main inhibitor of plasmin. It inhibits plasmin by forming a 1:1 stoichiometric complex with any free plasmin in the plasma and, therefore, prevents the binding of plasmin to fibrin and fibrinogen.

Which of the following statements is correct regarding the D-dimer test?

A. Levels are decreased in DIC

B. Test detects polypeptides A and B

C. Test detects fragments D and E

D. Test has a negative predictive value

D. Test has a negative predictive value

D The D-dimer assay evaluates fibrin degradation. It is a nonspecific screening test that is increased in many conditions in which fibrinolysis is increased, such as DIC and fibrinolytic therapy. The D-dimer test is widely used to rule out thrombosis and thrombotic activities. The negative predictive value of a test is the probability that a person with a negative result is free of the disease the test is meant to detect. Therefore, a negative D dimer test rules out thrombosis and hence further laboratory investigations are not required.

A protein that plays a role in both coagulation and platelet aggregation is:

A. Factor I

B. Factor VIII

C. Factor IX

D. Factor XI

A. Factor I

A Factor I (fibrinogen) is necessary for platelet aggregation along with the glycoprotein IIb/IIIa complex. Factor I is also a substrate in the common pathway of coagulation. Thrombin acts on fibrinogen to form fibrin clots.

A standard 4.5-mL blue-top tube filled with 3.0 mL of blood was submitted to the laboratory for PT and APTT tests. The sample is from a patient undergoing surgery the following morning for a tonsillectomy. Which of the following is the necessary course of action by the technologist?

A. Run both tests in duplicate and report the average result

B. Reject the sample and request a new sample

C. Report the PT result

D. Report the APTT result

B. Reject the sample and request a new sample

B A 4.5-mL blue-top tube contains 4.5 mL blood + 0.5 mL sodium citrate. The tube should be 90% full. A tube with 3.0 mL blood should be rejected as quantity not sufficient (QNS). QNS samples alter the necessary blood to an anticoagulant ratio of 9:1. The excess anticoagulant in a QNS sample binds to the reagent calcium, thereby resulting in prolongation of the PT and APTT.

Which statement is correct regarding sample storage for the prothrombin time test?

A. Stable for 24 hours if the sample is capped

B. Stable for 24 hours if the sample is refrigerated at 4°C

C. Stable for 4 hours if the sample is stored at 4°C

D. Should be run within 8 hours

A. Stable for 24 hours if the sample is capped

A According to Clinical Laboratory Standards Institute (CLSI, formerly NCCLS) guidelines, plasma samples for PT testing are stable for 24 hours at room temperature if capped. Refrigerating the sample causes cold activation of factor VII and, therefore, shortened PT results. The APTT samples are stable for 4 hours if stored at 4°C.

In primary fibrinolysis, the fibrinolytic activity results in response to:

A. Increased fibrin formation

B. Spontaneous activation of fibrinolysis

C. Increased fibrin monomers

D. DIC

B. Spontaneous activation of fibrinolysis

B Primary fibrinolysis is a rare pathological condition in which a spontaneous systemic fibrinolysis occurs. Plasmin is formed in the absence of coagulation activation and clot formation. Primary fibrinolysis is associated with increased production of plasminogen and plasmin, decreased plasmin removal from the circulation, and spontaneous bleeding

Plasminogen deficiency is associated with:

A. Bleeding

B. Thrombosis

C. Increased fibrinolysis

D. Increased coagulation

B. Thrombosis

B Plasminogen deficiency is associated with thrombosis. Plasminogen is an important component of the fibrinolytic system. Plasminogen is activated to plasmin, which is necessary for degradation of fibrin clots to prevent thrombosis. When plasminogen isdeficient, plasmin is not formed, causing a defect in the clot lysing processes

Which of the following clotting factors are activated by thrombin that is generated by tissue pathway (TF-VIIa)?

A. XII, XI

B. XII, I

C. I, II

D. V, VIII

D. V, VIII

D Factors V and VIII are activated by the thrombin that is generated by the action of TF-VIIa on factor X to form factor Xa. Factor Xa forms a complex with factor Va on the platelet surfaces. FXa -Va complex in the presence of phospholipid and Ca+2 transform more prothrombin to thrombin.

What substrate is used in a chromogenic factor assay?

A. p-nitroanaline

B. Chloropheonol red

C. Prussian blue

D. Ferricyanide

A. p-nitroanaline

A The chromogenic, or amidolytic, assays use a color-producing substance known as a chromophore. The chromophore used for the coagulation laboratory is p-nitroaniline (pNa). The pNa is bound to a synthetic oligopeptide substrate. The protease cleaves the chromogenic substrate at the site binding the oligopeptide to the pNA, which results in release of pNA. Free pNA has a yellow color; the color intensity of the solution is proportional to the protease activity and is measured by a photodetector at 405 nm

Which of the following antibodies is used in the D-dimer assay?

A. Polyclonal directed against X and Y fragments

B. Polyclonal directed against D-dimer

C. Monoclonal against D and E fragments

D. Monoclonal against D-dimer

D. Monoclonal against D-dimer

D The D-dimer is the fibrin degradation product generated by the action of plasmin on cross-linked fibrin formed by XIIIa. The patient plasma is mixed with latex particles coated with monoclonal antibodies against D-domains. The test can be automated or performed manually on a glass slide, looking macroscopically for agglutination. ELISA methods are also available. Normal D-dimer in plasma is less than 2 ng/mL. Increased levels of D-dimer are associated with DIC, thrombolytic therapy, venous thrombosis, and thromboembolic disorders.

The D-dimer assay has a 90% 95% negative predictive value, and has been used to rule out thrombosis and thromboembolic disorders.

2.2 Platelet and Vascular Disorders

Thrombotic thrombocytopenic purpura (TTP) is characterized by:

A. Prolonged PT

B. Increased platelet aggregation

C. Thrombocytosis

D. Prolonged APTT

B. Increased platelet aggregation

B Thrombotic thrombocytopenic purpura (TTP) is a quantitative platelet disorder associated with increased intravascular platelet activation and aggregation resulting in thrombocytopenia. The PT and APTT results are normal in TTP.

Thrombocytopenia may be associated with:

A. Postsplenectomy

B. Hypersplenism

C. Acute blood loss

D. Increased proliferation of pluripotential stem cells

B. Hypersplenism

B Hypersplenism is associated with thrombocytopenia. In this condition, up to 90% of platelets can be sequestered in the spleen, causing decreases in circulatory platelets. Postsplenectomy, acute blood loss, and increased proliferation of pluripotential stem cells are associated with thrombocytosis.

Aspirin prevents platelet aggregation by inhibiting the action of which enzyme?

A. Phospholipase

B. Cyclo-oxygenase

C. Tromboxane A2 synthetase

D. Prostacyclin synthetase

B. Cyclo-oxygenase

B Aspirin prevents platelet aggregation by inhibiting the activity of the enzyme cyclo-oxygenase. This inhibition prevents the formation of thromboxane A2 (TXA2), which serves as a potent platelet aggregator.

Normal platelet adhesion depends upon:

A. Fibrinogen

B. Glycoprotein Ib

C. Glycoprotein IIb, IIIa complex

D. Calcium

B. Glycoprotein Ib

B Glycoprotein Ib is a platelet receptor for VWF. Glycoprotein Ib and VWF are both necessary for a normal platelet adhesion. Other proteins that play a role in platelet adhesion are glycoproteins V and IX.

Which of the following test results is normal in a patient with classic von Willebrand's disease?

A. Bleeding time

B. Activated partial thromboplastin time

C. Platelet count

D. Factor VIII:C and von Willebrand's factor (VWF) levels

C. Platelet count

C Von Willebrand's disease is an inherited, qualitative platelet disorder resulting in increased bleeding, prolonged APTT, and decreased factor VIII:C and VWF levels. The platelet count and morphology are generally normal in von Willebrand's disease, but aggregation in the platelet function assay is

abnormal.

Bernard-Soulier syndrome is associated with:

A. Decreased bleeding time

B. Decreased factor VIII assay

C. Thrombocytopenia and giant platelets

D. Abnormal platelet aggregation to ADP

C. Thrombocytopenia and giant platelets

C Bernard-Soulier syndrome is associated with thrombocytopenia and giant platelets. It is a qualitative platelet disorder caused by the deficiency of glycoprotein Ib. In Bernard-Soulier syndrome, platelet aggregation to ADP is normal. Aggregation in the platelet function assay is abnormal. Factor VIII assay is not indicated for this diagnosis.

When performing platelet aggregation studies, which set of platelet aggregation results would most likely be associated with Bernard-Soulier syndrome?

A. Normal platelet aggregation to collagen, ADP, and ristocetin

B. Normal platelet aggregation to collagen, ADP, and epinephrine; decreased aggregation to ristocetin

C. Normal platelet aggregation to epinephrine and ristocetin; decreased aggregation to collagen and ADP

D. Normal platelet aggregation to epinephrine, ristocetin, and collagen; decreased aggregation to ADP

B. Normal platelet aggregation to collagen, ADP, and epinephrine; decreased aggregation to ristocetin

B Bernard-Soulier syndrome is a disorder of platelet adhesion caused by deficiency of glycoprotein Ib. Platelet aggregation is normal in response to collagen, ADP, and epinephrine but abnormal in response to ristocetin

Which set of platelet responses would be most likely associated with Glanzmann's thrombasthenia?

A. Normal platelet aggregation to ADP and ristocetin; decreased aggregation to collagen

B. Normal platelet aggregation to collagen; decreased aggregation to ADP and ristocetin

C. Normal platelet aggregation to ristocetin; decreased aggregation to collagen, ADP, and epinephrine

D. Normal platelet aggregation to ADP; decreased aggregation to collagen and ristocetin

C. Normal platelet aggregation to ristocetin; decreased aggregation to collagen, ADP, and epinephrine

C Glanzmann's thrombasthenia is a disorder of platelet aggregation. Platelet aggregation is normal in response to ristocetin, but abnormal in response to collagen, ADP, and epinephrine

Which of the following is a characteristic of acute immune thrombocytopenic purpura?

A. Spontaneous remission within a few weeks

B. Predominantly seen in adults

C. Nonimmune platelet destruction

D. Insidious onset

A. Spontaneous remission within a few weeks

A Acute immune thrombocytopenic purpura is an immune-mediated disorder found predominantly in children. It is commonly associated with infection (primarily viral). It is characterized by abrupt onset, and spontaneous remission usually occurs within several weeks

TTP differs from DIC in that:

A. APTT is normal in TTP but prolonged in DIC

B. Schistocytes are not present in TTP but are present in DIC

C. Platelet count is decreased in TTP but normal in DIC

D. PT is prolonged in TTP but decreased in DIC

A. APTT is normal in TTP but prolonged in DIC

A Thrombotic thrombocytopenic purpura is a platelet disorder in which platelet aggregation increases, resulting in thrombocytopenia. Schistocytes are present in TTP as a result of microangiopathic hemolytic anemia; however, the PT and APTT are both normal. In DIC, the PT and APTT are both prolonged, the platelet count is decreased, and schistocytes are seen in the peripheral smear.

Several hours after birth, a baby boy develops petechiae and purpura and a hemorrhagic diathesis. The platelet count is 18 × 109/L. What is the most likely explanation for the low platelet count?

A. Drug-induced thrombocytopenia

B. Secondary thrombocytopenia

C. Neonatal alloimmune thrombocytopenia

D. Neonatal DIC

C. Neonatal alloimmune thrombocytopenia

C Neonatal alloimmune thrombocytopenia is similar to the hemolytic disease of the fetus and newborn. It results from immunization of the mother by fetal platelet antigens. The offending antibodies are commonly anti HPA-1a alloantibodies that are directed against glycoproteins IIb/IIIa, Ib/IX, Ia/IIb, and CD 109. The maternal antibodies cross the placenta, resulting in thrombocytopenia in the fetus.

Which of the following is associated with post-transfusion purpura (PTP)?

A. Nonimmune thrombocytopenia/ alloantibodies

B. Immune-mediated thrombocytopenia/ alloantibodies

C. Immune-mediated thrombocytopenia/ autoantibodies

D. Nonimmune-mediated thrombocytopenia/ autoantibodies

B. Immune-mediated thrombocytopenia/ alloantibodies

B Post-transfusion purpura is a rare form of alloimmune thrombocytopenia characterized by severe thrombocytopenia following transfusion of blood or blood products. PTP is caused by antibody-related platelet destruction in previously immunized patients. In the majority of cases, the alloantibody produced is against platelet antigen A1 (PlA1), also referred to as HPA-1a.

Hemolytic uremic syndrome (HUS) is associated with:

A. Fever, thrombocytosis, anemia, and renal failure

B. Fever, granulocytosis, and thrombocytosis

C. Escherichia coli 0157:H7

D. Leukocytosis and thrombocytosis

C. Escherichia coli 0157:H7

C HUS is caused by E. coli 0157:H7. It is associated with ingestion of E. coli contaminated foods and is commonly seen in children. The clinical manifestations in HUS are fever, diarrhea, thrombocytopenia, microangiopathic hemolytic anemia, and renal failure.

Storage pool deficiencies are defects of:

A. Platelet adhesion

B. Platelet aggregation

C. Platelet granules

D. Platelet production

C. Platelet granules

C Storage pool deficiencies are defects of platelet granules. Most commonly, a decrease in platelet-dense granules is present with decreased release of ADP, ATP, calcium, and serotonin from platelet-dense granules.

Lumi-aggregation measures:

A. Platelet aggregation only

B. Platelet aggregation and ATP release

C. Platelet adhesion

D. Platelet glycoprotein Ib

B. Platelet aggregation and ATP release

B Lumi-aggregation measures platelet aggregation and ATP release. It is performed on whole blood diluted with saline. Platelet aggregation is measured by impedance, whereas ATP release is measured by addition of luciferin to a blood sample. There is no ATP release in storage pool deficiencies.

Neurological findings may be commonly associated with which of the following disorders?

A. HUS

B. TTP

C. ITP

D. PTP

B. TTP

B TTP is characterized by neurological problems, fever, thrombocytopenia, microangiopathic hemolytic anemia, and renal failure.

Which of the following is correct regarding acquired thrombotic thrombocytopenic purpura?

A. Autoimmune disease

B. Decreased VWF

C. Decreased platelet aggregation

D. Decreased platelet adhesion

A. Autoimmune disease

A Acquired TTP is an autoimmune disease associated with autoantibodies produced against VWF cleaving enzyme (ADAMTS-13). This deficiency results in an increase in plasma VWF and consequently increased platelet aggregation and thrombocytopenia

Hereditary hemorrhagic telangiectasia is a disorder of:

A. Platelets

B. Clotting proteins

C. Fibrinolysis

D. Connective tissue

D. Connective tissue

D Hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome) is a connective tissue disorder associated with telangiectases (dilated capillaries) of the mucous membranes and skin. Lesions may develop on the tongue, lips, palate, face, hands, nasal mucosa, and throughout the gastrointestinal tract. This disorder is an autosomal dominant condition that usually manifests in adolescence or early adulthood.

Which of the following prevents platelet aggregation?

A. Tromboxane A2

B. Tromboxane B2

C. Prostacyclin

D. Antithrombin

C. Prostacyclin

C Prostacyclin is released from the endothelium and is an inhibitor of platelet aggregation. Thromboxane A2

promotes platelet aggregation. Thromboxane B2 is an oxidized form of thromboxane A2 and is excreted in the urine. Antithrombin is a physiological anticoagulant.

Which defect characterizes Gray's syndrome?

A. Platelet adhesion defect

B. Dense granule defect

C. Alpha granule defect

D. Coagulation defect

C. Alpha granule defect

C Gray's syndrome is a platelet granule defect associated with a decrease in alpha granules resulting in decreased production of alpha granule proteins such as platelet factor 4 and beta thromboglobulin. Alpha granule deficiency results in the appearance of agranular platelets when viewed on a Wright'sstained blood smear.

The P2Y12 ADP receptor agonist assay may be used to monitor platelet aggregation inhibition to which of the following drugs?

A. Warfarin

B. Heparin

C. LMWH

D. Clopidogrel (Plavix)

D. Clopidogrel (Plavix)

D The VerifyNow P2Y12 test is used to assess a patient's response to antiplatelet drugs such as clopidogrel (Plavix) and prasugrel (Effient). These drugs are given orally for prevention of thrombosis along with aspirin, or as alternative antiplatelet drugs for patients who cannot tolerate or are not sensitive to aspirin. Clopidogrel and prasugrel prevent platelet aggregation by irreversibly binding to P2Y12, which is a platelet membrane receptor for ADP. The VerifyNow P2Y12 test is a whole blood test and uses ADP as an aggregating agent to measure the level of platelet aggregation impaired by these medications. The baseline platelet aggregation is established. The percent (%) change from baseline aggregation is calculated and reported as % P2Y12 inhibition

Which of the following instruments can be used to evaluate platelet function?

A. Platelet aggregometer

B. VerifyNow

C. PFA-100

D. All of the above

Platelet aggregometer, VerifyNow, PFA-100

D. All of the above

D All of the instruments listed can be used to evaluate platelet function. Platelet function testing is done to either determine the cause of bleeding in a patient with normal platelet count and normal coagulation tests, or to assess the efficacy of antiplatelet drugs.

Which of the following platelet aggregating agents demonstrates a monophasic aggregation curve when used in optimal concentration?

A. Trombin

B. Collagen

C. Adenosine diphosphate (ADP)

D. Epinephrine

B. Collagen

B Collagen is the only commonly used agent that demonstrates a single-wave (monophasic) response preceded by a lag time.

2.3 Coagulation System Disorders

The APTT is sensitive to a deficiency of which clotting factor?

A. Factor VII

B. Factor X

C. PF3

D. Calcium

B. Factor X

B The APTT is sensitive to the deficiency of coagulation factors in the intrinsic pathway (factors XII, XI, IX, and VIII) and the common pathway (factors X, V, II, and I).

Which test result would be normal in a patient with dysfibrinogenemia?

A. Thrombin time

B. APTT

C. PT

D. Immunologic fibrinogen level

D. Immunologic fibrinogen level

D The level of plasma fibrinogen determined immunologically is normal. In a patient with dysfibrinogenemia, fibrinogen is not polymerized properly, causing abnormal fibrinogen-dependent coagulation tests.

A patient with a prolonged PT is given intravenous vitamin K. The PT corrects to normal after 24 hours. What clinical condition most likely caused these results?

A. Necrotic liver disease

B. Factor X deficiency

C. Fibrinogen deficiency

D. Obstructive jaundice

D. Obstructive jaundice

D Obstructive jaundice contributes to coagulation disorders by preventing vitamin K absorption. Vitamin K is fat soluble and requires bile salts for absorption. Parenteral administration of vitamin K bypasses the bowel; hence the need for bile salts.

Which factor deficiency is associated with a prolonged PT and APTT?

A. X

B. VIII

C. IX

D. XI

A. X

A Factor X, a common pathway factor deficiency, is most likely suspected, because both PT and APTT are prolonged. Other causes may include liver disease, vitamin K deficiency, and anticoagulant drugs such as Coumadin and heparin

A prolonged APTT is corrected with factor VIII- deficient plasma but not with factor IX-deficient plasma. Which factor is deficient?

A. V

B. VIII

C. IX

D. X

C. IX

C Because the prolonged APTT is not corrected with a factor IX-deficient plasma, factor IX is suspected to be deficient in the test plasma.

Which of the following is a characteristic of classic hemophilia A?

A. Prolonged bleeding time

B. Autosomal recessive inheritance

C. Mild to severe bleeding episodes

D. Prolonged PT

C. Mild to severe bleeding episodes

C Hemophilia A (factor VIII deficiency) is characterized by mild to severe bleeding episodes, depending upon the concentration of factor VIII:C. Hemophilia A is inherited as a sex-linked disease. Bleeding time and prothrombin time are both normal in hemophilia A.

Refer to the following results:

PT = prolonged

APTT = prolonged

Platelet count = decreased

Which disorder may be indicated?

A. Factor VIII deficiency

B. von Willebrand's disease

C. DIC

D. Factor IX deficiency

C. DIC

C In DIC, there is a diffuse intravascular generation of thrombin and fibrin. As a result, coagulation factors and platelets are consumed, resulting in decreased platelet count and increased PT and APTT.

Which of the following is a predisposing condition for the development of DIC?

A. Adenocarcinoma

B. Idiopathic thrombocytopenic purpura (ITP)

C. Post-transfusion purpura (PTP)

D. Heparin-induced thrombocytopenia (HIT)

A. Adenocarcinoma

A Adenocarcinoma can liberate procoagulant (thromboplastic) substances that can activate prothrombin intravascularly. ITP is a thrombocytopenia caused by an autoantibody; PTP is an alloimmune thrombocytopenia caused by transfusion of blood or blood products; HIT results from an antibody to heparin-PF4 complex causing thrombocytopenia in 1%-5% of patients who are on heparin therapy. In some affected persons, thrombosis may also occur.

Factor XII deficiency is associated with:

A. Bleeding episodes

B. Epistaxis

C. Decreased risk of thrombosis

D. Increased risk of thrombosis

D. Increased risk of thrombosis

D Factor XII-deficient patients commonly have thrombotic episodes. Factor XII is the contact activator of the intrinsic pathway of coagulation. It also plays a major role in the fibrinolytic system by activating plasminogen to form plasmin. Hemorrhagic manifestations are not associated with factor XII deficiency because thrombin generated by the extrinsic pathway can activate factor XI to XIa, and factor VIIa/TF can activate factor IX to IXa

The following results were obtained on a patient:

normal platelet count and function, normal PT, and prolonged APTT.

Which of the following disorders is most consistent with these results?

A. Hemophilia A

B. Bernard-Soulier syndrome

C. von Willebrand's disease

D. Glanzmann's thrombasthenia

A. Hemophilia A

A Hemophilia A is associated with the deficiency of factor VIII resulting in bleeding and an abnormal APTT. The platelet number and function are normal in this disorder. Von Willebrand's disease is a disorder of platelet adhesion associated with decreased VWF and factor VIII, causing an abnormal platelet function test and an abnormal APTT test. Both Glanzmann's thrombasthenia and Bernard Soulier syndrome cause deficient platelet aggregation, but do not cause an abnormal APTT.

The following laboratory results were obtained from a 40-year-old woman:

PT = 20 sec; APTT = 50 sec; thrombin time = 18 sec.

What is the most probable diagnosis?

A. Factor VII deficiency

B. Factor VIII deficiency

C. Factor X deficiency

D. Hypofibrinogenemia

D. Hypofibrinogenemia

D Fibrinogen (factor I) is a clotting protein of the common pathway and is evaluated by the thrombin time. In hypofibrinogenemia (fibrinogen concentration

When performing a factor VIII activity assay, a patient's plasma is mixed with:

A. Normal patient's plasma

B. Factor VIII deficient plasma

C. Plasma with a high concentration of factor VIII

D. Normal control plasma

B. Factor VIII deficient plasma

B Coagulation factor assays are based upon the ability of the patient's plasma to correct any specific factor-deficient plasma. To measure for factor VIII activity in a patient's plasma, diluted patient plasma is mixed with a factor VIII-deficient plasma. An APTT test is performed on the mixture. Each laboratory should calculate its own normal ranges based on patient population, reagents, and the instrument used. An approximate range of 50%-150% is considered normal.

The most suitable product for treatment of factor VIII deficiency is:

A. Fresh frozen plasma

B. Factor VIII concentrate

C. Prothrombin complex concentrate

D. Factor V Leiden

B. Factor VIII concentrate

B Factor VIII concentrate (human or recombinant) is the treatment of choice for patients with factor VIII deficiency. Fresh frozen plasma contains factor VIII; however, it is no longer used as the primary treatment for factor VIII deficiency. Prothrombin complex concentrate is used to treat patients with factor VIII inhibitor.

Which of the following is associated with an abnormal platelet aggregation test?

A. Factor VIII deficiency

B. Factor VIII inhibitor

C. Lupus anticoagulant

D. Afibrinogenemia

D. Afibrinogenemia

D Fibrinogen is a plasma protein that is essential for platelet aggregation and fibrin formation. In afibrinogenemia, platelet aggregation is abnormal.

Refer to the following results:

PT = normal

APTT = prolonged

Bleeding time= increased

Platelet count = normal

Platelet aggregation to ristocetin = abnormal

Which of the following disorders may be indicated?

A. Factor VIII deficiency

B. DIC

C. von Willebrand's disease

D. Factor IX deficiency

C. von Willebrand's disease

C VWF is involved in both platelet adhesion and coagulation via complexing with factor VIII. Therefore, in von Willebrand's disease (deficiency or functional abnormality of VWF) factor VIII is also decreased, causing an abnormal APTT as well as abnormal platelet aggregation to ristocetin. The platelet count and the PT are not affected in VWF deficiency

Which results are associated with hemophilia A?

A. Prolonged APTT, normal PT

B. Prolonged PT and APTT

C. Prolonged PT, normal APTT

D. Normal PT and APTT

A. Prolonged APTT, normal PT

A Hemophilia A is associated with factor VIII deficiency. Factor VIII is a factor in the intrinsic coagulation pathway that is evaluated by the APTT and not the PT test. The PT test evaluates the extrinsic and common pathways.

Fibrin monomers are increased in which of the following conditions?

A. Primary fibrinolysis

B. DIC

C. Factor VIII deficiency

D. Fibrinogen deficiency

B. DIC

B Most of the clotting factors are made in the liver. Therefore, severe liver disease results in multiple factor deficiencies. An inherited disorder of coagulation is commonly associated with a single factor deficiency. Lupus anticoagulant is directed against the phospholipid-dependent coagulation factors. Dysfibrinogenemia results from an abnormal fibrinogen molecule

Which of the following is associated with multiple factor deficiencies?

A. An inherited disorder of coagulation

B. Severe liver disease

C. Dysfibrinogenemia

D. Lupus anticoagulant

B. Severe liver disease

B Most of the clotting factors are made in the liver. Therefore, severe liver disease results in multiple factor deficiencies. An inherited disorder of coagulation is commonly associated with a single factor deficiency. Lupus anticoagulant is directed against the phospholipid-dependent coagulation factors. Dysfibrinogenemia results from an abnormal fibrinogen molecule

Normal PT and APTT results in a patient with a poor wound healing may be associated with:

A. Factor VII deficiency

B. Factor VIII deficiency

C. Factor XII deficiency

D. Factor XIII deficiency

D. Factor XIII deficiency

D Factor XIII deficiency can lead to impaired wound healing and may cause severe bleeding problems. Factor XIII is a fibrin stabilizing factor that changes the fibrinogen bonds in fibrin polymers to stable covalent bonds. Factor XIII is not involved in the process of fibrin formation and, therefore, the PT and APTT are both normal

Fletcher factor (prekallikrein) deficiency may be associated with:

A. Bleeding

B. Thrombosis

C. Trhombocytopenia

D. Thrombocytosis

B. Thrombosis

B Fletcher factor (prekallikrein) is a contact factor. Activated prekallikrein is named kallikrein and is involved in activation of factor XII to XIIa. Like factor XII deficiency, Fletcher factor deficiency may be associated with thrombosis.

One of the complications associated with a severe hemophilia A is:

A. Hemarthrosis

B. Mucous membrane bleeding

C. Mild bleeding during surgery

D. Immune-mediated thrombocytopenia

A. Hemarthrosis

A In severe hemophilia A, factor VIII activity is less than 1%, resulting in a severe bleeding diathesis such as hemarthrosis (bleeding into the joints).

The most common subtype of classic von Willebrand's disease is:

A. Type 1

B. Type 2A

C. Type 2B

D. Type 3

A. Type 1

A VWF is a multimeric plasma glycoprotein that results in different subtypes of von Willebrand's disease with varied severity. The most common subtype is subtype 1, and 70%-80% of these cases are associated with mild bleeding. Subtype 3 involves the total absence of the von Willebrand's molecule and is associated with severe bleeding. Subtypes 2A and 2B result in deficiency of intermediate and/or high molecular weight portions of the von Willebrand molecule and are associated with 10%-12% and 3%-6% of cases of von Willebrand's disease, respectively.

A prolonged APTT and PT are corrected when mixed with normal plasma. Which factor is most likely deficient?

A. VIII

B. V

C. XI

D. IX

B. V

B Factor V (common pathway factor) deficiency is most likely suspected, because both the PT and APTT are prolonged, and both are corrected when mixed with normal plasma

2.4 Inhibitors, Thrombotic Disorders, and Anticoagulant Drugs

Which characteristic describes antithrombin (AT)?

A. It is synthesized in megakaryocytes

B. It is activated by protein C

C. It is a cofactor of heparin

D. It is a pathological inhibitor of coagulation

C. It is a cofactor of heparin

C Antithrombin is heparin cofactor and it is the most important naturally occurring physiological inhibitor of blood coagulation. It represents about 75% of antithrombotic activity and is an α2-globulin made by the liver.

Which laboratory test is affected by heparin therapy?

A. Thrombin time

B. Fibrinogen assay

C. Protein C assay

D. Protein S assay

A. Thrombin time

A Heparin is an antithrombin drug, and therefore increases the thrombin time test along with the APTT and PT. Heparin therapy has no effect on fibrinogen, protein C, or protein S assays. APTT is the test of choice for monitoring heparin therapy

An abnormal APTT caused by a pathological circulating anticoagulant is:

A. Corrected with factor VIII-deficient plasma

B. Corrected with factor IX-deficient plasma

C. Corrected with normal plasma

D. Not corrected with normal plasma

D. Not corrected with normal plasma

D In the presence of a pathological circulating anticoagulant, a mixing test using normal plasma does not correct the abnormal APTT. These anticoagulants are pathological substances and are endogenously produced. They are either directed against a specific clotting factor or against a group of factors. A prolonged APTT due to a factor deficiency is corrected when mixed with a normal plasma. Factors VIII and IX deficient plasmas are used for assaying factor VIII and IX activities, respectively.

The lupus anticoagulant affects which of the following tests?

A. Factor VIII assay

B. Factor IX assay

C. VWF assay

D. Phospholipid-dependent assays

D. Phospholipid-dependent assays

D The lupus anticoagulant interferes with phospholipid-dependent coagulation assays such as the PT and APTT tests. The lupus anticoagulant does not inhibit clotting factor assays, and does not inhibit in vivo coagulation.

Which statement about Coumadin (warfarin) is accurate?

A. It is a vitamin B antagonist

B. It is not recommended for pregnant and lactating women

C. It needs antithrombin as a cofactor

D. APTT test is used to monitor its dosage

B. It is not recommended for pregnant and lactating women

B Coumadin (warfarin) crosses the placenta and is present in human milk; it is not recommended for pregnant and lactating women. Warfarin is a vitamin K antagonist drug that retards synthesis of the active form of vitamin K-dependent factors (II, VII, IX, and X). Antithrombin is a heparin (not warfarin) cofactor. The International Normalized Ratio (INR) is used to monitor warfarin dosage.

Which statement regarding protein C is correct?

A. It is a vitamin K-independent zymogen

B. It is activated by fibrinogen

C. It activates cofactors V and VIII

D. Its activity is enhanced by protein S

D. Its activity is enhanced by protein S

D Protein S functions as a cofactor of protein C and as such enhances its activity. Activated protein C inactivates factors Va and VIIIa

Which of the following is an appropriate screening test for the diagnosis of lupus anticoagulant?

A. Thrombin time test

B. Diluted Russell's viper venom test (DRVVT)

C. D-dimer test

D. FDP test

B. Diluted Russell's viper venom test (DRVVT)

B Russell's viper venom (RVV) reagent contains factors X and V, activating enzymes that are strongly phospholipid dependent. The reagent also contains RVV, calcium ions, and phospholipid. In the presence of phospholipid autoantibodies such as lupus anticoagulant, the reagent phospholipid is partially neutralized causing prolongation of the clotting time. Thrombin time evaluates fibrinogen. FDP and D-dimer tests evaluate fibrinogen and fibrin degradation products.

Which of the following is most commonly associated with activated protein C resistance (APCR)?

A. Bleeding

B. Thrombosis

C. Epistaxis

D. Menorrhagia

B. Thrombosis

B Activated protein C resistance is the single most common cause of inherited thrombosis. In 90% of individuals, the cause is gene mutation of factor V (factor V Leiden). Affected individuals are predisposed to thrombosis, mainly after age 40. Heterozygous individuals may not manifest thrombosis unless other clinical conditions coexist

A 50-year-old man has been on heparin for the past 7 days. Which combination of the tests is expected to be abnormal?

A. PT and APTT only

B. APTT, TT only

C. APTT, TT, fibrinogen assay

D. PT, APTT, TT

D. PT, APTT, TT

D Heparin is a therapeutic anticoagulant with an antithrombin activity. Heparin also inhibits factors XIIa, XIa, Xa, and IXa. In patients receiving heparin therapy, the PT, APTT, and TT are all prolonged. Quantitative fibrinogen assay, however, is not affected by heparin therapy

Which of the following drugs inhibits ADP mediated platelet aggregation?

A. Heparin

B. Warfarin

C. Aspirin

D. Prasugrel

D. Prasugrel

D Prasugrel (Effient) is an antiplatelet drug that reduces platelet aggregation by irreversibly blocking the P2Y12 receptors on the platelet surface membrane, thereby inhibiting platelet aggregation to ADP. Aspirin is another antiplatelet drug that inhibits platelet aggregation by blocking the action of the enzyme cyclo-oxygenase. Warfarin and heparin are anticoagulant drugs that act against clotting factors

Thrombin-thrombomodulin complex is necessary for activation of:

A. Protein C

B. Antithrombin

C. Protein S

D. Factors V and VIII

A. Protein C

A Protein C is activated by thrombin-thrombomodulin complex. Thrombomodulin (TM) is a transmembrane protein that accelerates protein C activation 1,000-fold by forming a complex with thrombin. When thrombin binds to TM, it loses its clotting function, including activation of factors V and VIII. Activated protein C deactivates factors Va and VIIIa. Protein S is a cofactor necessary for the activation of protein C.

What test is used to monitor heparin therapy?

A. INR

B. APTT

C. TT

D. PT

B. APTT

B Heparin dosage may be monitored by the APTT test. Heparin dose is adjusted to an APTT of 1.5-2.5 times the mean of the laboratory reference ranges. This level of APTT is equivalent to plasma heparin levels of 0.3-0.7 U/mL. The PT would be prolonged in heparin therapy, but the test is not as sensitive as the APTT. Heparin inhibits thrombin, and therefore, causes a prolonged TT. The TT test, however, is not used to monitor heparin therapy.

What test is commonly used to monitor warfarin therapy?

A. INR

B. APTT

C. TT

D. Ecarin time

A. INR

A Warfarin is a vitamin K antagonist drug. It inhibits vitamin K-dependent factors (II, VII, IX, and X) and other vitamin K-dependent proteins such as proteins C and S. Warfarin therapy is monitored by the INR. An INR of 2.0-3.0 is used as the target when monitoring warfarin therapy for prophylaxis and treatment of DVT. A higher dose of warfarin (giving an INR of 2.5- 3.5) is required for patients with mechanical heart valves.

What clotting factors (cofactors) are inhibited by protein S?

A. V and X

B. Va and VIIIa

C. VIII and IX

D. VIII and X

B. Va and VIIIa

B Factors Va and VIIIa are deactivated by protein S and activated protein C.

Which drug promotes fibrinolysis?

A. Warfarin

B. Heparin

C. Urokinase

D. Aspirin

C. Urokinase

C Urokinase is a thrombolytic drug commonly used to treat acute arterial thrombosis. Urokinase can also be used for the treatment of venous thromboembolism, myocardial infarction, and clotted catheters. Warfarin and heparin are anticoagulant drugs, whereas aspirin prevents platelet aggregation by inhibiting cyclo-oxygenase.

Diagnosis of lupus anticoagulant is confirmed by which of the following criteria?

A. Decreased APTT

B. Correction of the APPT by mixing studies

C. Neutralization of the antibody by high concentration of platelets

D. Confirmation that abnormal coagulation tests are time and temperature dependent

C. Neutralization of the antibody by high concentration of platelets

C The International Society of Hemostasis and Thrombosis has recommended four criteria for the diagnosis of lupus anticoagulant: (1) a prolongation of one or more of the phospholipid-dependent clotting tests such as APTT or DRVVT; (2) the presence of an inhibitor confirmed by mixing studies (not corrected); (3) evidence that the inhibitor is directed against phospholipids by neutralizing the antibodies with a high concentration of platelets (platelet neutralization test or DRVVT with platelet-rich plasma); (4) lack of any other causes for thrombosis. Lupus inhibitor is not commonly time or temperature dependent.

Which of the following abnormalities is consistent with the presence of lupus anticoagulant?

A. Decreased APTT/bleeding complications

B. Prolonged APTT/thrombosis

C. Prolonged APTT/thrombocytosis

D. Thrombocytosis/thrombosis

B. Prolonged APTT/thrombosis

B Lupus anticoagulant interferes with phospholipids in the APTT reagent, resulting in prolongation of APTT. However, in vivo, lupus anticoagulant decreases fibrinolytic activity, causing an increased risk of thrombosis. Lupus anticoagulant does not result in a bleeding tendency unless there is a coexisting thrombocytopenia or other coagulation abnormality.

Which of the following is a characteristic of low molecular weight heparin (LMWH)?

A. Generally requires monitoring

B. Specifically acts on factor Va

C. Has a longer half-life than unfractionated heparin

D. Can be used as a fibrinolytic agent

C. Has a longer half-life than unfractionated heparin

C Low molecular weight heparin (LMWH) is a small glycosaminoglycan that is derived from unfractionated heparin (UFH). The LMWH has a low affinity for plasma proteins and endothelial cells and therefore has a longer half-life. The half-life of the drug does not depend on the dosage. LMWH has an inhibitory effect on factors Xa and IIa. It does not require routine monitoring except in patients with renal failure, obese patients, pediatric patients, and pregnant patients.

Which of the following tests is most likely to be abnormal in patients taking aspirin?

A. Platelet morphology

B. Platelet count

C. Bleeding time

D. Prothrombin time

C. Bleeding time

C Aspirin is an antiplatelet drug. It prevents platelet aggregation by inhibition of cyclo-oxygenase. Aspirin has no effect on the platelet count, platelet morphology, or prothrombin time

Which of the following is associated with antithrombin deficiency?

A. Thrombocytosis

B. Thrombosis

C. Thrombocytopenia

D. Bleeding

B. Thrombosis

B Antithrombin is a physiological anticoagulant. It inhibits factors IIa, Xa, IXa, XIa, and XIIa. Deficiency of antithrombin is associated with thrombosis. Thrombotic events may be primary (in the absence of a triggering factor) or may be associated with another risk factor such as pregnancy or surgery.

Which of the following may be associated with thrombotic events?

A. Decreased protein C

B. Increased fibrinolysis

C. Afibrinogenemia

D. ITP

A. Decreased protein C

A Protein C is a physiological inhibitor of coagulation. It is activated by thrombin thrombomodulin complex. Activated protein C inhibits cofactors Va and VIIIa. The deficiency of protein C is associated with thrombosis. Increased fibrinolysis, afibrinogenemia, and ITP are associated with bleeding

Aspirin resistance may be associated with:

A. Bleeding

B. Factor VIII deficiency

C. Thrombosis

D. Thrombocytosis

C. Thrombosis

C Up to 22% of patients taking aspirin become resistant to aspirin's antiplatelet effect. Patients who are aspirin resistant have a higher risk of thrombosis (heart attacks and strokes).

A prolonged thrombin time is indicative of which of the following antithrombotic therapies?

A. Prasugrel

B. Clopidogrel

C. Aspirin

D. Heparin

D. Heparin

D Heparin is an antithrombin drug causing prolonged TT in patients who are on heparin therapy. Prasugrel, clopidogrel, and aspirin are antiplatelet drugs causing inhibition of platelet aggregation.

Screening tests for thrombophilia should be performed on:

A. All pregnant women because of the thrombotic risk

B. Patients with a negative family history

C. Patients with thrombotic events occurring at a young age

D. Patients who are receiving anticoagulant therapy

C. Patients with thrombotic events occurring at a young age

C Laboratory tests for evaluation of thrombophilia are justified in young patients with thrombotic events, in patients with a positive family history after a single thrombotic event, in those with recurrent spontaneous thrombosis, and in pregnancies associated with thrombosis.

Prothrombin G20210A is characterized by which of the following causes and conditions?

A. Single mutation of prothrombin molecule/ bleeding

B. Single mutation of prothrombin molecule/ thrombosis

C. Decreased levels of prothrombin in plasma/ thrombosis

D. Increased levels of prothrombin in plasma/ bleeding

B. Single mutation of prothrombin molecule/ thrombosis

B Prothrombin G20210A is defined as a single-point mutation of the prothrombin gene, resulting in increased concentration of plasma prothrombin and thereby a risk factor for thrombosis. Prothrombin G20210A is the second most common cause of inherited hypercoagulability (behind factor V Leiden). It has the highest incidence in whites from southern Europe. The thrombotic episodes generally occur before age 40.

Factor V Leiden promotes thrombosis by preventing:

A. Deactivation of factor Va

B. Activation of factor V

C. Activation of protein C

D. Activation of protein S

A. Deactivation of factor Va

A Factor V Leiden is a single-point mutation in the factor V gene that inhibits factor Va inactivation by protein C. Activated protein C enhances deactivation of factors Va and VIIIa

What is the approximate incidence of antiphospholipid antibodies in the general population?

A.

B. 2%

B The incidence of antiphospholipid antibodies in the general population is about 2%.

Which of the following laboratory tests is helpful in the diagnosis of aspirin resistance?

A. APTT

B. PT

C. Platelet count and morphology

D. Platelet aggregation

D. Platelet aggregation

D Currently, the platelet aggregation test is considered the gold standard for evaluation of aspirin resistance. In aspirin resistance, platelet aggregation is not inhibited by aspirin ingestion. Aspirin resistance has no effect on platelet count and morphology

Which of the following complications may occur as a result of decreased tissue factor pathway inhibitor (TFPI)?

A. Increased hemorrhagic episodes

B. Increased thrombotic risk

C. Impaired platelet plug formation

D. Immune thrombocytopenia

B. Increased thrombotic risk

B Tissue factor pathway inhibitor (TFPI) is released from the vasculature and is the most important inhibitor of the extrinsic pathway. TFPI inhibits factors Xa and VIIa-TF complex. Therefore, the deficiency of TFPI is associated with thrombosis.