Tuesday, August 17, 2010

Activated Partial Thromboplastin Time(aPTT)

Activated Partial Thromboplastin Time(aPTT)



aPTT is the best screening test for disorders of coagulation; it is abnormal in 90% of patients with coagulation disorders. Screens for all coagulation factors that contribute to thrombin except factor VII and XII. The test may not detect mild clotting defects which seldom cause significant bleeding.


Normal range

25 – 38 seconds

Indications and Interpretation

Monitor heparin therapy; Screen for hemophilia A and B,

Prolonged by

Defect in following factors: I, II, V, VIII, IX, X, XI, XII; Presence of specific inhibitors of clotting factors (most frequently antibody against factor VIII, in 15% of patients with hemophilia); heparin, warfarin and lupus anticoagulant.

Normal in

 Thrombocytopenia, Platelet dysfunction, Von Willebrand's disease, isolated defects of factor VII.

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