SAMMC Departments: Coumadin

Patient Information

Coumadin

Monitoring Coumadin with Blood Testing

Associated with life threatening bleeding. Nature has managed this threat by evolving an elaborate clotting system which responds to any injury by forming a clot to seal off the damaged blood vessels (using a host of different proteins in combination with blood cells called platelets). Thus any medication which alters the normal function of this natural protective mechanism must be carefully administered and monitored.

Vitamin K in the diet is normally absorbed by the liver and used as a necessary factor in the production of key clotting proteins. As these proteins circulate in the blood, they provide a potential defense against bleeding through an opening in a damaged blood vessel. Coumadin® impairs the production of these liver-dependent clotting proteins. As the concentration of these proteins in the blood decreases, the blood takes longer to clot. This is the basis for the anticoagulant action of Coumadin®.

It has been known for a long time that the dose needed for 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.

When treating a patient with Coumadin®, it is best to manage the medication according to the INR ratio. For most clinical conditions, an INR of 2.5 to 3.0 indicates the appropriate dosage. INR values above 5.0 can be dangerous. INR values of 1.0 indicate no Coumadin® effect at all.

When first starting therapy with anticoagulation, it is important to obtain frequent blood tests in order for proper the dosage to be determined. Your treating physician will review the INR result, and increase or decrease the dosage of medication to reach the "target range." Most patients will be asked to have their blood test drawn twice a week initially. As the dose becomes more routine, the testing intervals can be spaced out. If you take your medication only at night, the physician can conveniently make an adjustment in your dosage on the same day as the blood test. Otherwise, the dosage must be altered starting on the following day. After each dose change, another INR test is recommended in 2 to 3 days to monitor the result of the new dosage.

Most blood testing labs will still draw blood from a vein in your arm. This is the most reliable and traditional source for obtaining blood for the INR test. However, there are now some laboratories which have the capability to use droplets of blood from a finger tip puncture. For some patients, this is less emotional and/or painful. Ask the technician in your doctors office or clinical laboratory if they have the "finger-stick" INR assay available.

The most important advice on INR testing is follow up. As a patient on a powerful blood thinning medication, you should continue to work with one physician who takes charge of the dosing of this medication. The INR results and the new dosage should be available to you within 24 hours of your blood draw. In addition, you should come back for further INR tests after any dosage adjustment is made. If any other medications are added or removed from you regimen, it is best to recheck the INR to make sure that the body's handling of Coumadin® has not been affected in any way.

Gradually, as you are taking Coumadin® for a longer period of time, it is possible to take the drug without frequent blood tests. Once a steady dosage schedule is finally reached, most patients administer the same dose for long periods of time without blood testing. Some physicians will keep their patients on a schedule of every 3 months for repeat testing. However, more frequent testing is indicated if the patient develops a serious infection, new illness, is started or withdrawn from medications which affect Coumadin®, etc.

If you have any questions about how often your blood tests should be performed, or what INR target range is being used for treatment of your condition, then please address these questions to your treating physician.

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Coumadin Information

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