Coumadin dosage is adjusted as a result of INR. If INR is too high, then Coumadin is decreased.
Coumadin is an anticoagulant which is used to lower the chance of blood clots. Vitamin K in the diet is normally absorbed by the liver and used as a necessary factor in the production of key clotting proteins. Coumadin impairs the production of liver-dependent clotting proteins. As the concentration of these proteins in the blood decreases, the blood takes longer to clot.
The dose needed for therapeutic blood thinning is different in each patient. The rate of absorption of the drug, the dietary Vitamin K load, and the livers response to Coumadin does vary from person to person. In order to obtain the clinical anticoagulant effect without overdosage (and subsequent bleeding complications), laboratory tests have been used to monitor the results of Coumadin in each patient.
For many years, the principal test used to monitor the Coumadin effect was the Prothrombin Time (PT). The International Normalized Ratio (INR) was developed to reduce variability in Pro-Time results. The INR standardizes the methods for comparison amongst different laboratories.
A patient treated with Coumadin is best managed according to the INR ratio. INR values of 1.0 indicate no Coumadin effect at all. For most clinical conditions, an INR of 2.5 to 3.0 is an appropriate target range. For patients who have a high risk of clot formation, the INR needs to be higher - about 2.5 to 3.5. INR values above 5.0 can be dangerous.
Most clinical laboratories still report the Pro-Time result along with the INR value, and most doctors and patients still refer to the blood testing as "getting a Pro-Time". However, Coumadin dosage is adjusted according to INR more often than to the Pro-Time result.