Prothrombin time (PT)
A deficiency of Vitamin K may be suspected and is usually discovered when unexpected or excessive bleeding occurs. In such cases, a prothrombin time is the main laboratory test performed to investigate the bleeding. If the result is prolonged and is suspected to be due to low levels of vitamin K, then vitamin K will often be given by injection. If the bleeding stops and the PT/INR returns to normal, then a vitamin K deficiency is assumed to be the cause.
Other coagulation tests may occasionally be performed to evaluate someone with symptoms of excessive bleeding and bruising such as PTT, thrombin time, platelet count, platelet function tests, coagulation factor tests, fibrinogen, and d-dimer.
Measurements of vitamin K level in the blood are rarely used to determine if a deficiency exists. Since this is not a routine test, it is usually sent to a reference laboratory, and results may take several days.