Disorders of Primary Hemostasis: Types, Diagnosis, and Management

What is the primary cause of bleeding in disorders of primary hemostasis?

Defects in the formation of an adequate platelet plug on an injured blood vessel wall.

What are the three categories of defects that prevent platelet plug formation?

Quantitative disorders, qualitative disorders, or defects of the blood vessel wall.

How do inherited primary hemostatic disorders typically present?

A history of childhood bleeding, such as gingival bleeding or easy/spontaneous bruising.

What are the typical clinical manifestations of primary hemostasis abnormalities?

Skin or mucosal bleeding, including epistaxis, gingival bleeding, GI bleeding, menorrhagia, or hematuria.

Which clinical features distinguish secondary hemostasis defects from primary hemostasis defects?

Spontaneous hemarthrosis and hematomas of deep structures.

Why is the automated platelet count the most important initial test for primary hemostasis?

Because acquired quantitative platelet disorders are the most common disorders of primary hemostasis.

What is pseudothrombocytopenia?

A falsely low automated platelet count caused by platelet satellitism or clumping.

What is the cause of EDTA-dependent pseudothrombocytopenia?

IgG antibodies that bind to the platelet membrane glycoprotein IIb/IIIa complex in the presence of EDTA.

What is the modern replacement for the traditional bleeding time test?

The PFA-100.

Which medications are known to cause a prolonged bleeding time?

Aspirin and non-steroidal analgesics.

Which four assays must be performed together to evaluate for von Willebrand's disease?

Factor VIII coagulant activity, vWF:Ag, ristocetin-induced platelet aggregation, and von Willebrand's multimers.

What does platelet aggregation testing measure?

The response of platelets to stimuli such as epinephrine, ADP, collagen, and ristocetin.

What hormone regulates platelet production?

Thrombopoietin (TPO).

Where is thrombopoietin primarily produced?

The liver, and to a lesser extent, the spleen.

What happens to TPO levels during thrombocytopenia?

Plasma concentration of TPO increases to boost megakaryocyte and platelet production.

At what platelet count level do clinical signs and symptoms of thrombocytopenia usually manifest?

Below 100 x 10³/μL.

At what platelet count level is overt spontaneous hemorrhage usually seen?

Less than 20 x 10³/μL.

What are the three distinct mechanisms of quantitative platelet disorders?

Deficient platelet production, abnormal platelet distribution, and increased platelet destruction.

What is a myelophthisic picture on a peripheral smear?

The presence of nucleated red cells, tear-drop shaped cells, and immature granulocytes, indicating bone marrow infiltration.

What laboratory finding is associated with the intramedullary death of hematopoietic progenitors in ineffective erythropoiesis?

High serum lactate dehydrogenase (LDH) levels.

How does alcohol affect platelet production?

It has a direct toxic effect on the bone marrow, producing thrombocytopenia.

What is the inheritance pattern of Wiskott-Aldrich syndrome?

X-linked (occurs only in males).

What fraction of platelets is normally pooled in the spleen?

Approximately 1/3.

What is the result of platelet sequestration in an enlarged spleen?

Thrombocytopenia (hypersplenism).

What is Kasabach-Merritt syndrome?

A rare disorder resulting in platelet sequestration in giant hemangiomas.

What is the primary purpose of bone marrow aspiration and biopsy in platelet disorders?

To determine the etiology of quantitative platelet disorders.

What is the primary cause of Idiopathic Thrombocytopenic Purpura (ITP)?

Autoantibodies directed against the patient's own platelets.

How is a diagnosis of ITP typically confirmed?

It is a diagnosis of exclusion, as there is no single definitive test.

What is the typical clinical course of childhood ITP?

It is usually self-limiting, with spontaneous remission occurring in 6-8 weeks.

What are the common clinical manifestations of adult ITP?

Mucosal bleeding, such as menorrhagia, epistaxis, easy bruisability, or petechiae.

What is the typical bone marrow finding in adult ITP?

Increased or normal numbers of megakaryocytes.

Why are platelets in ITP often morphologically large on a peripheral smear?

They reflect early release from the marrow in response to peripheral destruction.

What is the long-term treatment of choice for adult ITP?

Splenectomy.

What is the mechanism of action of corticosteroids in treating ITP?

They reduce autoantibody production and suppress splenic sequestration of sensitized platelets.

What is the primary target antigen in Posttransfusion Purpura (PTP)?

The P1A1 (HPA-1a) antigen.

Who is most at risk for developing Posttransfusion Purpura?

Individuals (typically middle-aged women) who lack the P1A1 antigen on their platelets.

What is the primary cause of mortality in infants with Isoimmune Neonatal Thrombocytopenia?

Intracranial hemorrhage.

What is the suggested role of the HLA-B8 antigen in Isoimmune Neonatal Thrombocytopenia?

It may protect against maternal immunization, accounting for the disorder's relatively low incidence.

What is the recommended delivery method for suspected Isoimmune Neonatal Thrombocytopenia to prevent birth trauma?

Cesarean delivery.

How does a drug act as a hapten in drug-induced immune thrombocytopenia?

It complexes with a larger carrier molecule to elicit an antibody response.

Which drugs are most frequently implicated in drug-induced immune thrombocytopenia?

Quinine, quinidine, salicylates, thiazides, and sulfa drugs.

What is the typical timeframe for purpura to appear after initial drug exposure in drug-induced thrombocytopenia?

Approximately 7 days.

What are the two distinct types of heparin-associated thrombocytopenia?

A benign early-onset type and a severe type associated with thrombosis (HITTS).

What does the acronym HITTS stand for?

Heparin-induced thrombocytopenia and thrombosis syndrome.

What is the pathological mechanism of HITTS?

Antibodies produced against the heparin-platelet factor 4 complex cause Fc receptor-induced platelet activation.

What is the primary screening test for HITTS antibodies?

ELISA (Enzyme-linked immunosorbent assay).

Why are platelet transfusions often ineffective in ITP?

Transfused platelets are usually rapidly destroyed by the circulating autoantibodies.

What is the role of Rituximab in treating ITP?

It is an anti-CD20 monoclonal antibody used for patients refractory to primary treatment.

What is the clinical significance of younger platelets in ITP regarding bleeding time?

They may be more adequate at maintaining hemostasis, explaining why bleeding time is not always as prolonged as expected.

What is the primary treatment for hemorrhagic complications in Posttransfusion Purpura?

Plasmapheresis and gamma globulin.

What is the recommended platelet transfusion strategy for infants with Isoimmune Neonatal Thrombocytopenia?

Use of maternal platelets or P1A1-negative donor platelets.

What is the immediate clinical action required upon diagnosis of HITTS?

Discontinuation of heparin.

What immunoassay is used to screen for antibodies in HITTS?

ELISA

How does optical density (OD) in ELISA relate to HITTS?

Higher OD values indicate a higher likelihood of HITTS presence.

What is the first step in managing a patient with HITTS?

Discontinue heparin.

How long does it take for the platelet count to normalize after discontinuing heparin in HITTS?

4 to 6 days.

Why is warfarin use cautioned in HITTS patients?

It may increase the risk of skin necrosis and venous limb gangrene.

What is hirudin?

A leech-derived peptide with antithrombin activity used as an anticoagulant.

What is a major clinical risk associated with hirudin use?

High risk of bleeding.

Which hematologic malignancies are associated with secondary immune thrombocytopenia?

Hodgkin's disease, non-Hodgkin's lymphoma, and chronic lymphocytic leukemia.

What percentage of SLE patients develop thrombocytopenia resembling ITP?

Approximately 14%.

How do viral infections typically affect platelet production?

They may transiently impair megakaryopoiesis without reducing marrow cellularity.

What is the primary mechanism of thrombocytopenia in bacterial sepsis?

Immune response, potentially with or without disseminated intravascular coagulation (DIC).

How does HIV-related immune thrombocytopenic purpura differ from classic ITP?

The pattern of IgG subclasses and the level of anti-IgG immune complexes on platelet surfaces are significantly different.

What is the reported effect of mRNA COVID-19 vaccines on platelet counts?

They can cause rapid-onset, severe thrombocytopenia that responds to ITP treatment.

What is the classic pentad of signs and symptoms for TTP?

Thrombocytopenia, microangiopathic hemolytic anemia, fever, neurologic abnormalities, and renal dysfunction.

Which diagnostic procedure is helpful when TTP diagnosis is in question?

Biopsy of superficial arterioles and capillaries from the skin or gingiva.

What two factors following endothelial damage contribute to thrombosis in TTP?

Inhibition of fibrinolysis and deficiency of prostacyclin (PGI2) synthesis.

What is the female-to-male ratio for TTP incidence?

3:2.

What laboratory findings indicate hemolysis in TTP?

Increased LDH and indirect bilirubin, and decreased haptoglobin levels.

Why should platelet transfusions be avoided in TTP unless the patient is bleeding?

They may exacerbate microangiopathy and are linked to clinical deterioration and death.

What is the current treatment of choice for TTP?

Plasma exchange.

What is the role of Rituximab in TTP management?

It is used after clinical remission to preemptively prevent relapses.

What are the three clinical hallmarks of Hemolytic Uremic Syndrome (HUS)?

Microangiopathic hemolytic anemia, thrombocytopenia, and renal failure.

What is the typical cause of HUS in pediatric patients?

Bacterial infections (E. coli or Shigella) that secrete toxins damaging endothelial cells.

Where are thrombi typically localized in HUS?

Glomerular capillaries and afferent arterioles of the kidney.

What is the difference between acute and chronic DIC regarding platelet counts?

Acute DIC usually presents with thrombocytopenia, while chronic DIC may show normal, elevated, or decreased platelet counts.

What is the underlying mechanism common to all forms of DIC?

Accelerated platelet destruction combined with coagulation factor consumption.

What is the typical platelet count range for gestational thrombocytopenia?

50-80 x 10³/μL

What is the treatment for gestational thrombocytopenia?

No treatment is necessary; platelet counts return to normal after delivery.

What are the clinical hallmarks of preeclampsia?

Hypertension, elevated uric acid, and thrombocytopenia.

What does the acronym HELLP stand for in the context of eclampsia variants?

Hemolysis, Elevated Liver Enzymes, Low Platelets

What medication appears useful in treating preeclampsia?

Aspirin

What is the primary difference in platelet count between reactive thrombocytosis and primary myeloproliferative neoplasms?

Reactive thrombocytosis rarely exceeds 1000 x 10³/μL.

What is a common cause of mild reactive thrombocytosis that is corrected by iron repletion?

Iron deficiency anemia (IDA)

Why does thrombocytosis often occur after a splenectomy?

The spleen is thought to produce a humoral factor that regulates thrombopoiesis.

Which drug is specifically noted to be associated with drug-related thrombocytosis?

Epinephrine

Which growth factors are administered to stimulate platelet production after chemotherapy?

Interleukin-11 and thrombopoietin

What is the genetic inheritance pattern of Glanzmann's thrombasthenia?

Autosomal-recessive

Which membrane complex is absent or deficient in Glanzmann's thrombasthenia?

GPIIb/IIIa complex

What is the function of the GPIIb/IIIa complex on activated platelets?

It mediates the binding of fibrinogen, vWF, and fibronectin, and facilitates clot retraction.

What are the diagnostic criteria for Glanzmann's thrombasthenia regarding platelet aggregation?

Absent aggregation to ADP, thrombin, collagen, and epinephrine, with normal agglutination to ristocetin.

What is a major risk of repeated platelet transfusions in Glanzmann's patients?

Development of alloantibodies to GPIIb/IIIa or anti-HLA antibodies, leading to refractoriness.

What therapy is useful for controlling menorrhagia in Glanzmann's patients?

Estrogen therapy (birth control pills)

Which membrane complex is deficient in Bernard-Soulier syndrome?

GPIb/IX complex

What is the primary role of the GPIb/IX/V receptor?

It mediates vWF-dependent adhesion of platelets to subendothelium at high shear rates.

What is the characteristic platelet morphology in Bernard-Soulier syndrome?

Large, irregularly shaped platelets (giant platelets).

How does the ristocetin-induced aggregation test differ between Bernard-Soulier and von Willebrand's disease?

In von Willebrand's, it is corrected by adding normal plasma; in Bernard-Soulier, it is not.

What are the diagnostic criteria for Bernard-Soulier regarding platelet aggregation?

Absent aggregation to human vWF and ristocetin, but normal aggregation to ADP, collagen, and epinephrine.

What is the typical treatment for active bleeding in Bernard-Soulier syndrome?

Red blood cell transfusions and an antifibrinolytic agent.