All are to assess platelet functions EXCEPT:
ANSWER: (A) Prothrombin timeREF: Wintrobe's hematology 11ed page 1242Tests for platelet function:Bleeding time: Hemostasis in a small superficial wound, such as that produced when measuring the bleeding time, depends on the rate at which a stable platelet plug is formed and, thus, provides a measure of the efficiency of the vascular and platelet phases. However, it does not discriminate between vascular defects, thrombocytopenia, and platelet dysfunction.Platelet enumerationPlatelet volume measurementsPlatelet aggregationClot Retraction: Clot retraction usually is deficient when the platelet count is below 50,000/pl and in a rare disorder of platelet function (Glanzmann thrombasthenia). It is normal in most other disorders of platelet function. This test is primarily of historical interest; Glanzmann thrombasthenia is typically diagnosed using platelet aggregation methods or flow cytometer.Tests of Coagulation Phase:Partial thromboplastin time: The PTT is a simple test of the intrinsic and common pathways of coagulation. When a mixture of plasma and a phospholipid platelet substitute is recalcified, fibrin forms at a normal rate only if the factors involved in the intrinsic pathway (prekallikrein, high-molecular-weight kininogen, and factors XII, XI, IX, and VIII) and in the common pathway (factors X and V, prothrombin, and fibrinogen) are present in normal amounts. The PTT is somewhat more sensitive to deficiencies of factors VIII and IX than to deficiencies of factors XI and XII or factors involved in the common pathwayProthrombin time The production of fibrin by means of the extrinsic and common pathways requires tissue factor and factor VII, in addition to factors X and V, Prothrombin, and fibrinogenThromboplastin generation test: The thromboplastin generation test is important for historical reasons. This two-stage test measures the amount and rate of prothrombinase formation by way of the intrinsic pathwayAssay of plasma fibrinogenInterpretation of Common Tests of Hemostasis and Blood CoagulationTestNormal Range a (+-2 SD) and ReferenceCommon Causes of AbnormalitiesPlatelet count Phase microscopy Automated Thrombocytopenia, thrombocytosis140,000-440,000/ul177,000-406,000/ulPartial thromboplastin time (activated)*26-37 secDeficiencies or inhibitors of prekallikrein; high- molecular-weight kininogen; factors XII, XI, IX, VIII, X, and V: Prothrombin or fibrinogen; lupus inhibitors; heparinProthrombin time*12.0-15.5 secDeficiencies or inhibitors of factors VII, X, and V; prothrombin or fibrinogen; dysfibrinogenemia; lupus inhibitors; heparinThrombin time*18-22 secA/dys/hypo/hyper-fibrinogenemia; inhibitors of thrombin (heparin) or fibrin polymerization (fibrin degradation products, Para proteins)Fibrinogen assay*150-430 mg/dlAfibrinogenemia, dysfibrinogenemia, and hypofibrinogenemia; inhibitors of thrombin or fibrin polymerizationFactor VIII assay*50-150 U/dlHemophilia A and von Willebrand disease; acquired antibodies to factor VIIIFibrin degradation product assay0-5 ug/mlDisseminated intravascular coagulation; fibrinogenolysis; thrombolytic drugs, liver disease;DysfibrinogenemiaNOTE: (*) mark signifies tests affected by heparin
Prothrombin time
Bleeding time
Clot retraction time
Prothrombin deactivation