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Hematology

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Which of the following is the finding in functional defect in platelets? (AIPG 2011)



A Normal platelet counts and prolonged Bleeding time.

B Normal platelet count and bleeding time.

C Prolonged bleeding time, Prothrombin time and PTT.

D Thrombocytopenia and prolonged bleeding time.

Ans. A

Normal platelet counts and prolonged Bleeding time.

(Robbin, Pathology, 7th ed., 649)

Classification of congenital disorder of platelet function:

1. Defects in platelet-vessel wall interaction (disorders of adhesion)

a. von Willebrand disease (deficiency or defect in plasma vWF)

b. Bernard-Soulier syndrome (deficiency or defect in GPIb)

2. Defects in platelet-platelet interaction (disorders of aggregation)

a. Congenital afibrinogenemia (deficiency of plasma fibrinogen)

b. Glanzmann thrombasthenia (deficiency or defect in GPIIb-IIIa)

3. Disorders of platelet secretion and signal transduction

4. Defects of Platelet Secretion

a. Congenital

i. Wiskott-Aldrich syndrome

b. Platelet coating (e.g., paraprotein, penicillin)

c. Decreased cyclooxygenase activity

i. Drug-induced (aspirin, nonsteroidal anti-inflammatory agents)

ii. Inherited

d. Granule storage pool defects

i. Inherited

ii. Acquired

e. Nonspecific drug effects (Heparin beta blocker, Dextran)

f. Uremia

5. Disorders of platelet coagulation - protein interaction

a. Defect in factor Va-Xa interaction on platelets (Scott syndrome)

Extra Edge:

Prolongation of BT indicates defect in platelet number or/and function.

BT is the best test for screening of platelet function.

Clot retraction test is more specific test for assessing its function.

BT is prolonged in thrombocytopenia and platelet dysfunction, vW disease.

Bernard Soulier disease

'Bernard - Soulier platelets react normally to all stimuli except Ristocetin'

'Platelet aggregation is normal in response to standard agonists (Collagen, ADP, Thrombin), but platelets fail to aggregate in response to ristocetin'

In functional defect in platelets, platelet counts and prolonged Bleeding time are normal .

1. A prolonged bleeding time in a patient with a normal platelet count is indicative of a qualitative platelet abnormality, von Willebrand disease, or afibrinogenemia.

2. A prolonged bleeding time in a patient with a normal platelet count suggests a diagnosis of von Willebrand disease or a disorder of platelet function (Platelet functional defect).

Disorder

Platelet count

Bleeding time

PT

PTT

Thrombocytopenia

Hemophilia A or B

DIC

Vitamin K Defiancy

Bemard-Sonlier Disease

Glamzmann’s Thrombasthenia

Extra Edge:

1. Thrombocytopenia = < 100,000/mm3.

2. Platelet count must reach a very low value (15,000–20,000/mm3) before generalized bleeding occurs;

3. The PFA-100, an instrument that measures platelet-dependent coagulation under flow conditions, is more sensitive and specific for platelet disorders and vWD than the bleeding time.

4. PT (extrinsic)––factors II, V, VII, and X.

5. PTT (intrinsic)––all factors except VII.

6. Bernard-Soulier disease = defect of platelet adhesion ( GP Ib).

7. Glanzmann’s thrombasthenia = defect of platelet aggregation (GP IIb-IIIa).

Hematology Flashcard List

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