Medical Laboratory Science Review: Coagulation | Quizlet

Platelets are produced from what cell?

Megakaryocytes

Platelet distribution

30% Spleen, 70% peripheral blood

Platelet reference range

150,000-400,000/mm3

Platelet life span

9-12 days

Platelet functions

initial arrest of bleeding and formation of the platelet plug

Adhesion

Glycoprotein Ib binds to exposed collagen, requires von Willebrands factor, results in release of ADP and other granule components (factor V and fibrinogen)

Aggregation

Platelets are stimulated by ADP to undergo shape change to exposethe glycoprotein IIb/ IIIa complex which binds fibrinogen. Fibrinogen binding links the platelets (first and reversible phase). The aggregates can disassociate.

Localization of the platelet plug

Secreting platelets release arachidonic acid which converts to prostaglandin, becomes thromboxane A2 in the platelet. Arachidonic acid is processed by adjacent endothelial cellsto form platelet-inhibiting prostacyclin

Fibrin clot

Platelets release fibrinogen, factor V and factor VIII. Fibrinogen is bound on the platelet surface . Factor 8 is bound to the platelet surface with vWf. Shape change exposes the phospholipid membrane for the assembly of factor complexes.

platelet III

binds factor 8 and 9a complex and requires Ca++. Binds factor V and Xa also requires Ca++.

Hemophila

difficiency in factor 8 (A) or 9a (B)

Plasma coagulation factors function

Substrate- Factor I
Cofactors (accelerate enzymatic reactions)- Factors II, V, VIII, high molecular weight kininogen

plasma coagulation factors enzymes

serine preoteases- sleave peptide bonds (factors II, VII,IX,X,XI and XII)
Transamidase- XIII only

Contact proteins

Factors XII, XI, PK and HMWK

Contact protein characteristics

participate in the initial phase of the intrinsic system. Not consumed during clotting and not vitamin K dependent.

Prothrombin proteins

factors II, VII, IX, X

Prothrombin protein characteristics

Vitamin K dependent, not consumed durin clotting (except II) present in plasma and serum

Fibrinogen proteins

Factors I, V, VIII, XIII

Fibrinogen protein characteristics

consumed during clotting (not in serum), high in acute phase (pregnancy and inflammation)

How fibrin is turned on

activated instrinsically by the collagen contact system. Activated extrinsically by disrupted endothelial cell membrane complex with factor VII to directly activate factor X

Cofactors used to stabilize fibrin

Factor VIII is bound with activated factor IX by calcium to the platelet phospholipid membrane. These factors activate factor X. this prothrombase complex converts prothrombin to the active thrombin.

How thrombin is crosslinks fibrin

cleaves peptides off of the fibrinogen molecule which polymerizes to form insoluble fibrin strands. Thrombin also activates factor XIII which crosslinks the fibrin strands at the D region (D-dimer).

Other functions of thrombin

Feeds back to potentiate factors V and VIII. Recruits and aggregates platelets. Turns on endothelial cell thrombomodulin to activate factors V and VIII

Turning off the cascade

Heparan sulfate on the endothelial cell binds antithrombin which activates the activated serine proteases. Activated protein C and its cofactor protein S inactivates factors VIII and V.

Turning on the fibrinolytic system

activated intrinsically by collagen via factor XXI/contact pathway that initiates intrinsic clotting or extrinsically by tissue plasminogen activator. Activators convert the precursor plasminogen into plasmin.

What does the Plasmin do?

Plasmin cleaves fibrin strands to soluble fragments of fibrin. Can come from fibrin clot or unclotted finbrinogen. D-dimer comes from crosslinked clot.

How to turn off the fibrinolytic system

Tissue plasminogen activator is inactivated by tissue plasminogen activator inhibitor. Active plasmin inhibited by alpha-2-Plasmin inhibitor if it escapes the area of the clot. This prevents fibrinogenolysis.

What tube is a coag sample collected in?

Sodium Citrate. Calcium is used for coagulation and platelet aggregation studies.

Ratio of blood to anticoagulant

9:1

Prothrombin Time (PT)

Screen for extrinsic and common pathways. Measures factors I, II, V, VII and X. Monitors anticoagulants. Reagents are tissue thromboplastin and CaCl2. Sensitive to Vit. K factors.

INR formula

(patient result (PT)/ Mean of reference range)ISI

INR Reference range

<13 seconds. Therapeutic goal 2.0-3.5.

Activated partial thromboplastin time APTT

Screen for intrinsic and common pathways. Measures all factors except VII and XIII. Monitors heparin therapy. Reagents- activator, platelet phospholipid and CaCl2

APTT reference range

20-40 secs. Therapeutic goal 1.5-2.5.

Fibrinogen assay

Factor I

Fibrinogen assay reference range

200-400 mg/dl

Thrombin Time

Does not measure defects in intrinsic/extrinsic pathways. Affected by low fibrinogen levels and presence of heparin and other antithrombins.

Thrombin Time reference range

<20 secs

Bleeding time

Measures platelet function and numbers. Prolonged with aspirin and other drugs. Not offered in many labs due to low sensitivity.

Bleeding time reference range

forearm normal: 2-9 minutes

clot retraction

evaluates platelet function, finbrinogen, red cell volume and fibrinolytic activity.

errors in clot retraction

abnormal if platelets <100,000. Anemia and hypofibrinogenemia low clot retraction. Rapid clot retraction indicates high fibrinolytic activity. Glansmann's Thromboasthenia

platelet aggregation

Necessary for platelets to stick to each other. Measured with aggregating reagents and photo-optics.

How platelet aggregation is measured with photo optics

As platelets aggregate, the turbidity of platelet rich plasma decreases. Samples kept at room temperature and then are heated to body temp before testing. Stirring is necessary to bring platelets in contact for aggregation to occur.

Aspirin destroys...

...cyclooxygenase. Inhibits secondary wave of aggregation.

Factor Assays

PT and APTT performed with specific factor deficient plasma. % activity and amount of correction with normal plasma determined. Range 40-150%

Russell's viper venom

Stypven time differentiates factor VII deficiency from common pathway deficiency. Factor VII deficient plasma demonstrates normal results.

Anti-factor Xa Assay

Monitors low molecular weight heparin therapy. The APTT is insensitive to LMWH

Reptilase time

Snake venom enzyme. Test similar to thrombin time, but is not inhibited by heparin. RR 18-22 seconds

Fibrinolysis testing

Fibrin/fibrinogen degradation. Latex beads coated with anti-fibrin. Latex D-dimer- monoclonal antibody to crosslinked D fragment. Positive in DIC, DVT, and pulmonary embolism.

Hemophilia A

Deficiency of factor VIII, Sex-linked recessive, Spontaneous bleeding into joints, treat with commercial Factor VIII.

Hemophilia B

Deficiency of factor IX, sex-linked recessive, clinically identical to A, treat with factor IX concentrates.

Hemophilia C

Deficiency of factor XI, incomplete autosomal recessive, wide range in clinical severity, high incidence in Jews, only contact factor associated with bleeding.

von Willebrand's Disease

Primary defect in vWF, usually secondary deficiency of factor VIII, autosomal dominant, platelet adhesion defect in prolonged bleeding time, treat with cryoprecipitate or DDAVP

Factor XIII deficiency

Autosomal recessive. not detected by common coagulation tests, results in a significant bleeding disorder, detected with the 5M urea test

Lupus Anticoagulant

Directed against phospholipids, seen in Lupus Erythematosis but also in malignancies, infections, drug therapy, and autoimmune disorders. Screening tests use low concentration of phospholipid reagents (Dilute Russel's Viper Venom). Use platelet neutralization techniques to confirm presence. Can prolong the APTT. Predisposes patient to clotting.

Factor VIII inhibitor

Most common specific inhibitor, but others have been demonstrated. APTT mixing studies differentiate between factor deficiency from inhibitor.

Vitamin K deficiency

functional deficiency of factors II, VII, IX, and X.

Liver Disease

Deficiency of factors I, II, V, VII, IX, and X. Factor VII deficiency most pronounced. Low clearance of plasminogen activators, high FDP due to fibrinolysis.

Disseminated Intravascular Coagulation

Secondary to sepsis or obstetric complications. Thrombotic occlusion of microcirculation. RBC fragments. Consumption of platelets and factors I, V, VIII. High levels of FDP and D-Dimer.

Arterial events

Platelet driven (arthlerosclerosis, prosthetic heart devices)

Venous events

blood flow problems, clot inhibitor deficiency.

antithrombin

Principle antagonist of active coagulation proteases. Produced in the liver. Activated by heparin sulfate on the endothelial cell and by heparin as a therapeutic drug.

Protein C

Vitamin K dependent serine protease. Activated by thrombomodulin on the endothelial cell. Requires Protein S cofactor. Inactivates Factors V and VIII.

Protein S

Vitamin K dependent. Cofactor for Protein C. Bound and free state. Only free protein S is functional so measure total and free.

Factor V Leiden

Mutation factor V. Resists the action of Protein C/S. Activated Protein C Resistance test.

Antiphospholipid syndrome

Any of the three classes of antibodies. Anticardiolipin antibodies. Lupus anticoagulant. Specific antibodies.

Prothrombin Mutation

Mutation at position 20210. 1-2% of general population are heterozygotes. Results in high throbin formation. Higher risk of thrombotic events.

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

Tissue Factor

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

XIIa

The anticoagulant of choice for most routine coagulation studies is

sodium citrate

Which ratio of anticoagulant to blood is correct?

1:9

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

both prolonged

What reagents are used in the PT test?

Thromboplastin and calcium

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

PT and APTT

Which clotting factor is not measured by PT and APTT?

Factor XIII

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

Thrombin time

Which of the following characterizes vitamin K?

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

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

It detects late degradation products (D and E)

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

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

Which coagulation tests would be abnormal in a vitamin K deficient patient?

PT and APTT

What is correct regarding the international normalized ratio (INR)?

It standardizes PT results

Which is referred to as an endogenous activator of plasminogen?

Tissue plasminogen activator

Which protein is the primary inhibitor of the fibrinolytic system?

a2-Antiplasmin

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

Test has a negative predictive value

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

Factor I

A standard 4.5 mL blue top tube is 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 is the necessary course of action by the technologist?

Reject the sample and request a new sample

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

Stable for 24 hrs if the sample is capped

In primary fibrinolysis, the fibrinolytic activity results in response to

Spontaneous activation of fibrinolysis

Plasminogen deficiency is associated with

Thrombosis

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

V, VIII

What substrate is used in a chromogenic factor assay?

p-nitroanaline

Which antibodies are used in the D-dimer assay?

Monoclonal against D-dimer

Thrombotic thrombocytopenia purpura (TTP) is characterized by

increased platelet aggregation

Thrombocytopenia may be associated with

Hypersplenism

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

Cyclo-oxygenase

Normal platelet adhesion depends upon

Glycoprotein Ib

Which test results is normal in a patient with classic con Willebrand's disease?

Platelet count

Bernard-Soulier syndrome is associated with

Thrombocytopenia and giant platelets

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

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