Tests are historically performed on 20 normal donors not on anticoagulants and 60 patients who have been on oral anticoagulant treatment for at least 6 weeks. Prothrombin Times are performed in duplicate for each Thromboplastin and the mean for each pair of tests derived. human against human, rabbit against rabbit etc. The calibration of a test Thromboplastin must be against a reference Thromboplastin of the same species e.g. Subsequent WHO IRPs contain no adsorbed bovine plasma.

The first WHO IRP was a human brain extract to which adsorbed bovine plasma was added to optimise the content of the non-vitamin K dependent coagulation factors - adsorption with Al(OH) 3 removes all the vitamin K dependent proteins]. The first WHO reference Thromboplastin was assigned an ISI of 1.0 and it is against this (and subsequent reference preparations) that all other Thromboplastin are calibrated. Individual Thromboplastins can be calibrated against an International WHO reference Thromboplastin (International Reference Preparation or IRP) to assign them an International Sensitivity Index or ISI. This difference in sensitivities is known as the sensitivity index. rabbit, human, bovine etc) used in the assay. The Prothrombin Time (PT) in an individual with one or more deficiencies of a clotting factor will vary with the type of Thromboplastin (e.g. Good luck.International Sensitivity Index & The International Normalised Ratio In that case, treat the underlying condition, if possible, while also treating the symptoms (if possible). Now, some liver conditions create a coagulopathy that can cause the coags (PT, PTT, INR) to elevate. It takes about 5 days off the Coumadin in order for the INR to return to 1. If the pt is taking Coumadin and the INR comes back 4, the dosage of Coumadin is usually decreased a little, and the test repeated, say, in a week to a month, depending on how well the anticoagulation clinic knows this particular pt and his/her patterns of response to Coumadin. In our cath lab, we usually don't cath a pt if the INR is greater than 1.5-1.7, as the risk of hemorrhage from the punctured artery is increased (let's not increase risk to the patient from doing the exam!). An INR of three means the blood takes about three times as long to clot compared with the normal value for that pt. If the pt is taking Coumadin (warfarin) to anticoagulate for a mechanical heart valve, the therapeutic INR should be around 3. An INR of 1 means the blood clots 'normally' for that pt. The greater the INR, the longer it takes the blood to clot. (please note the subtle difference between 'normal' and 'normal range.' if the lab's normal pt is 14, normal range might be 12-16).ĭoes this help? Do I need to clarify anything? If the pt's pt is 28 and the lab's normal is 14, then the inr is 2. So if the pt's pt is 14, and the lab's normal is 14, then the inr is 1. Inr is pt's pt divided by the labs normal. That 'inappropriate adjustment' could have serious consequences. So if your pt sample was sent to lab x one week, where their normal is 12 sec, and to lab z the next week, where their normal is 14 sec, there might be an inappropriate adjustment in your therapy if the difference in reference ranges isn't noted. It was developed because coumadin really doesn't have a wide therapeutic range, and as i mentioned above, different labs have different normals. Inr stands for international normalized ratio. What you posted seemed about right, but I would have to look it up. These goals also vary from facility to facility, but are generally similar. Similarly, you want a higher pt/inr for mechanical heart valve patients that for someone who is receiving coumadin for a-fib. For example, you want a higher ptt if a patient is receiving heparin for a dvt or pe than if it is for cardiac reasons. Goals for pt/inr and ptts vary according to why the patient is on the anticoagulant. You are correct in that pt/inr is used to monitor coumadin therapy, and ptt is used to monitor heparin therapy. Very important to check the normal ranges for the lab that did the test ). (this, by the way, is true for most every test. Ok, you are going to get different 'norms' because different labs use different machines and reagents, and have different normal ranges.

Inr normal range vs therapeutic