First investigation to be done in a patient with thrombocytopenia: September 2008

Ans. A: Platelet count Platelet count is the initial investigation to be done in all the cases of thrombocytopenia, followed by hemoglobin and WBC count. The prothrombin time (PT) and its derived measures of prothrombin ratio (PR) and international normalized ratio (INR) are measures of the extrinsic pathway of coagulation. They are used to determine the clotting tendency of blood, in the measure of warfarin dosage, liver damage, and vitamin K status. The reference range for prothrombin time is usually around 12-15 seconds; the normal range for the INR is 0.8-1.2. PT measures factors II, V, VII, X and fibrinogen. It is used in conjunction with the activated paial thromboplastin time (aPTT) which measures the intrinsic pathway.