Prothrombin time REF: Wintrobe's hematology lied page 1242 Tests 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 enumeration Platelet volume measurements Platelet aggregation Clot Retraction: Clot retraction usually is deficient when the platelet count is below 50,000411 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: Paial 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 re-calcified, 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 pathway Prothrombin 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 fibrinogen Thromboplastin generation test: The thromboplastin generation test is impoant for historical reasons. This two-stage test measures the amount and rate of prothrombinase formation by way of the intrinsic pathway Assay of plasma fibrinogen Interpretation of Common Tests of Hemostasis and Blood Coagulation Test Normal Range a (+-2 Common Causes of Abnormalities SD) and Reference Platelet count Thrombocytopenia, thrombocytosis Phase microscopy 140,000-440,000/u1 Automated 177,000-406,000/111 Paial thromboplastin 26-37 sec Deficiencies or inhibitors of prekallikrein; high? time(activated)* molecular-weight kininogen; factors XII, XI, IX, VIII, X, and V; Prothrombin or fibrinogen; lupus inhibitors; heparin Prothrombin time* 12.0-15.5 sec Deficiencies or inhibitors of factors VII, X, and V; prothrombin or fibrinogen; dysfibrinogenemia; lupus inhibitors; heparin Thrombin time* 18-22 sec A/dys/hypo/hyper-fibrinogenemia; inhibitors of thrombin (heparin) or fibrin polymerization (fibrin degradation products, Para proteins) Fibrinogen assay* 150-430 mg/dl Afibrinogenemia, dysfibrinogenemia, and hypofibrinogenemia; inhibitors of thrombin or fibrinpolymerization Factor VIII assay* 50-150 U/dl Hemophilia A and von Willebrand disease; acquired antibodies to factor VIII Fibrin degradation 0-5 pg/m1 Disseminated intravascular coagulation; fibrinogenolysis; product assay thrombolytic drugs, liver disease; Dysfibrinogenemia NOTE: (1 mark signifies tests affected by heparin