Which is most likely to be increased in Vit K deficiency: (DNB Dec 2010)
Vitamin K Deficiency
1. Hemorrhagic disease of new born results from a deficiency of vitamin K.
2. Prothrombin time is the single best laboratory test to detect vitamin K deficiency as vitamin K deficiency may present with isolated prolongation of PT.
3. Lab features of vit K deficiency
a. Both PT and PTT are prolonged but prolongation of PT is a more sensitive test to detect vit K deficiency than PTT
b. The PT is prolonged to a greater extent than PTT
c. With mild vit K deficiency only the PT is defective
d. Fibrinogen level, thrombin time and platelet count are not affected.
Extra Edge: (Ref. Hari-18th ed. Pg. 999)
To calculate the INR, the patient's PT is divided by the mean normal PT, and this ratio is then multiplied by the international sensitivity index (ISI), an index of the sensitivity of the thromboplastin used for PT determination to reductions in the levels of the vitamin K–dependent clotting factors.
Highly sensitive thromboplastins have an ISI of 1.0.
Most current thromboplastins have ISI values that range from 1.0 to 1.4.