Prothrombin Times and INR values

brs0660

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The chart below that tells how the normal value is calculated when one is on warfarin. The values do vary somewhat depending upon the lab doing the testing

Normal values may vary from lab to lab. A method of standardizing prothrombin time results, called the international normalized ratio (INR) system, has been developed so the results among labs using different test methods can be understood in the same way. Using the INR system, treatment with blood-thinning medicine (anticoagulant therapy) will be the same.

In some labs, only the INR is reported and the PT is not reported.

Prothrombin time (PT)Normal:
10–13 seconds
International normalized ratio (INR):
1.0–1.4

The warfarin (Coumadin) dose is changed so that the prothrombin time is longer than normal (by about 1.5 to 2.5 times the normal value or INR values 2 to 3).

Prothrombin times are also kept at longer times for people with artificial heart valves, because these valves have a high chance of causing clots to form.

Quest Diagnostics
 

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