AIIMS November 2011 – MCQ 88

Which of the following is true regarding prothrombin time measurement?
A. Should be measured within 2 hours of obtaining the sample
B. Sample should be refrigerated immediately to preserve coagulant factor function
C. Platelet rich plasma is required
D. Activation is done with kaolin

Correct answer : A. Should be measured within 2 hours of obtaining the sample

The plasma should be assayed withing four hours of blood collection.
Ref: Basic medical laboratory techniques By Barbara H. Estridge, Anna P. Reynolds, Norma J. Walters (via google books)

The specimen for measurement of prothrombin time should not be refrigerated.
Ref: Understanding clinical investigations: a quick reference manual By Susan Skinner (via google books)

Platelet rich plasma is not used of measurement of PT. Instead, tissue factor is used.
Ref: Guyton 11th p467

Kaolin is used for APTT measurement.