How is it calculated?
The INR is derived from prothrombin time (PT) which is calculated as a ratio of the patient's PT to a control PT standardized for the potency of the thromboplastin reagent developed by the World Health Organization (WHO) using the following formula:
INR = Patient [PT ÷ Control PT]ISI
In healthy people an INR of 1.1 or below is considered normal. An INR range of 2.0 to 3.0 is generally an effective therapeutic range for people taking warfarin for disorders such as atrial fibrillation or a blood clot in the leg or lung
What can affect INR?
In addition to vitamin K, any major lifestyle changes can cause your INR level to change. These can range from changing what foods you eat to how much you exercise. Major diet changes, such as starting a new diet or taking new supplements, can cause your INR level to fluctuate.
6). Platelet factor assay
7). Measurement of D-dimers (Fibrinolytic) degradation products.
Disseminated of intravascular coagulation
In this disorder, activated pro-coagulants are released into circulation. Platelets and coagulation factors are consumed and fibrin is deposited in the small vessel activating the fibrinolysis system.
The plasmin formed degrades the fibrin (also some fibrinogen) resulting in the buildup of FDPs in the circulation. The FDPs act as anticoagulants interfering with platelet function and fibrin stabilization. Therefore in DIC, the APTT and TT are prolonged and platelet count is reduced.
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