Lab test for patient on warfarin

 # A patient on warfarin sodium following myocardial infarction reports for an oral surgical procedure. Which one of the following laboratory tests should be preferred to ascertain the fitness? 
a. Prothrombin time 
b. Torniquet time 
c. clotting time 
d. bleeding time 

The correct answer is A. Prothrombin time.

The PT and INR tests measure the time it takes for blood to clot by forming thrombin. They evaluate the extrinsic and common coagulation pathways, screening for the presence or absence of fibrinogen (F I), prothrombin (F II), and F V, F VII, and F X. The normal range of PT is approximately 11–13 seconds. Because of individual laboratory reagent variability and the desire to be able to reliably compare the PT from one laboratory with that from another, the PT test is commonly reported with the INR. The INR, introduced by the World Health Organization in 1983, is the ratio of PT that adjusts for the sensitivity of the thromboplastin reagents, such that a normal coagulation profile is reported as an INR of 1.0, and higher values indicate abnormal coagulation. Its most common use is to measure the effects of VKAs and reduction of the vitamin K–dependent F II, F VII, F IX, and F X. It is not effective for hemophilias A and B, since it does not measure F VIII or F IX. Although most patients on VKAs are monitored by monthly venous blood draws and laboratory analysis, the CoaguChek system allows Clinical Laboratory Improvements Amendments (CLIA)-waived point-of-care PT/INR testing of fingerstick blood in physicians’ and dentists’ offices.

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