Tests in clotting disorders

The following are some tests ordered when assessing/diagnosing some clotting diseases.

Platelet tests:

A normal platelet count would yield ~ 150 – 400 x 10^9 /L platelets.

Bleeding time (BT) evaluates the platelet function up to the formation of the temporary platelet thrombus (primary hemostasis). A normal bleeding time is around 2 – 7 mins.

Platelet aggregation tests look at the aggregation response in response to regents such as ADP, adrenaline, collagen and ristocetin (induces platelet aggregation).

Tests for von Willebrand  factor (vWF) include ristocetin cofactor activity or vWF antigen assays. Ristocetin cofactor activity evaluates the function of vWF, where as the assays measures the quantity of vWF present in the serum.

Coagulation tests:

Prothrombin time (PT) assesses the extrinsic and common coagulation pathway. It involves factors VII, X, II and I. A normal PT is around 11 to 15 seconds. PT is commonly used to evaluate liver synthetic function, detect factor VII deficiency or monitor patients who are on warfarin.

The International normalized ratio (INR) is a value derived from PT, used as a standard to monitor patients on warfarin. While varying with the condition, a normal INR target for warfarin patients is between 2-3.

The activated Partial Thromboplastin Time (aPTT) evaluates the intrinsic and common pathway. The factors involved are XII, XI, IX, VIII, X,V,II,I. The normal reference interval would be 25-40 seconds. It is most commonly used to monitor heparin anticoagulation therapy. It’s also used to detect factor deficiencies in the intrinsic coagulation system.

Fibrinolytic sytem tests:

Fibrin(ogen) degradation products (FDP) are used to detect fragments associated with the plasmin degradation of fibrinogen or insoluble fibrin in the fibrin clots.

D-Dimer assays are specific tests that determine degradation of cross-linked fibrin monomers only. It does not detect fibrinogen degradation products as they do not form cross-links. It’s of particular clinical use when assessing deep vein thrombosis, pulmonary thromboembolisms and disseminated intravascular coagulation.


Goljan Rapid review Pathology 4th edition

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