# Medical question? Anyone know what INR stands for?

Discussion in 'General International Discussion' started by jocognito, Apr 8, 2002.

1. ### jocognito Junior Member

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hi folks,
hopefully this is one of the things the site is used for....if not sorry for abusing it.

does anyone know what INR in relation to blood test results stand for? i am still in pre-clinicals so have no idea what it means? thanks for all those experienced minds out there.

3. ### BellKicker Twisted Miler

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International Ratio, from what I've been told. As I'm sure you know, it's comparable from lab to lab, whereas PT and PTT are not. Hence international.

4. ### BellKicker Twisted Miler

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Okay, maybe some more info would be in place. I was so excited I could finally answer a question on here (I'm usually the learner here).

PT and PTT measure how long it takes for blood to clot. It's an arbitrary analysis so you can't compare one lab's results with another's.

INR is a reciprocical (sp?) value of clotting factors. Don't ask me the specifics. But it's reciprocical, so the higher it is, the thinner the blood. This comparable to measuring clotting factors, where a high value would indicate blood that was just waiting to coagulate.

A high INR could come from medication (anti-thrombus and so on) or from liver damage, as all the clotting factors (except Von Willebrand factor) are made in the liver.

I hope that was about right. Maybe someone will correct me if it's way off base.

5. ### Stormreaver The Blade of Tyshalle

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Just a bit of a refinement of DaneMD's answer:

INR=International Normalized Ratio

INR is used in relation to PT and is defined as observed PT/standard PT for the lab. Since the standard PT varies from lab to lab, the INR provides a convenient way to measure the degree of anticoagulation.

INR is used most often to regulate Warfarin (Coumadin) therapy, wherein the INR has to be kept within a certain range for a certain condition. While the INR would certainly be elevated in liver damage, it is not to be used as a guide to therapy there because of confounding factors.

Cheers.

6. ### Samoa Physician Pharmacist

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The reason PT values are different from lab to lab is that the thromboplastin reagent used varies in strength from supplier to supplier, and I think batch to batch as well. So they standardize each batch to an international standard (the ISI rating), and use this value as the exponent in the conversion equation. (PT observed/PT normal for the lab)^ISI.

7. ### bold and beautiful Member

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As stated above INR is ued to regulate coumadin or warfarin therapy The best dose of warfarin (or of any medicine, for that matter) is the lowest dose that accomplishes the desired result.

Considerable research is still going on to determine this dose for warfarin. The problem is difficult because the problems that come with too little warfarin are so bad that it is not ethical to give a dose that has much chance of being too low. On the other hand, higher doses of warfarin are clearly associated with higher risks of major bleeding that can be life-threatening. Current medical thinking relies on the International Normalized Ratio, or INR, of the blood test called the prothrombin time.

The INR is calculated mathematically in a way that corrects for differences in the method used for measuring the prothrombin time. It makes the results more comparable from place to place and at different times in the same place. The INR is a ratio of a clotting time compared to "normal". A normal person would have an INR of about 1.0. People with atrial fibrillation are often told to maintain an INR of 2.0 to 3.0. People with artificial valves and other reasons to have a strong reason to develop dangerous blood thrombi (like clots, but inside the body) are often advised to maintain an INR of 2.5 to 3.5. Newer research suggests that sometimes the INR can be maintained at a lower level (that is, closer to 1.5), but each person should consult his or her own physician about the best INR for him or her.

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