International normalized ratio
The result (in seconds) for a prothrombin time performed on a normal individual will vary according to the type of analytical system employed. This is due to the variations between different batches of manufacturer's tissue factor used in the reagent to perform the test. The INR was devised to standardize the results. Each manufacturer assigns an ISI value (International Sensitivity Index) for any tissue factor they manufacture. The ISI value indicates how a particular batch of tissue factor compares to an international reference tissue factor. The ISI is usually between 1.0 and 2.0. The INR is the ratio of a patient's prothrombin time to a normal (control) sample, raised to the power of the ISI value for the analytical system used.
INR = (PTtest/PTnormal) ISI (ISI je eksponent, PT su vremena zavisna od proizvođača opreme - trombostata)
Interpretation
The prothrombin time is the time it takes plasma to clot after addition of tissue factor (obtained from animals such as rabbits, or recombinant tissue factor, or from brains of autopsy patients). This measures the quality of the extrinsic pathway (as well as the common pathway) of coagulation. The speed of the extrinsic pathway is greatly affected by levels of functional factor VII in the body. Factor VII has a short half-life and the carboxylation of its glutamate residues requires vitamin K. The prothrombin time can be prolonged as a result of deficiencies in vitamin K, warfarin therapy, malabsorption, or lack of intestinal colonization by bacteria (such as in newborns). In addition, poor factor VII synthesis (due to liver disease) or increased consumption (in disseminated intravascular coagulation) may prolong the PT.
A high INR level such as INR=5 indicates that there is a high chance of bleeding, whereas if the INR=0.5 then there is a high chance of having a clot. Normal range for a healthy person is 0.9–1.3, and for people on warfarin therapy, 2.0–3.0, although the target INR may be higher in particular situations, such as for those with a mechanical heart valve, or bridging warfarin with a low-molecular weight heparin (such as enoxaparin) perioperatively.
Dakle, matematika nije jednostavna - ne znamo vremena ni korekcioni faktor proizvodjaca opreme ISI. Ali sta ce nam to, idemo dalje, razmisljamo pozitivno...
Ajd da dodam još malčice....
PTnormal = 10 - 12 sec; Za nas pod terapijom odnos PTnormal/PTtest = 0,15 - 0,27 ili 15 - 27% od normalnog vremena. 15 % bi odgovaralo INR=4,3, a 27% INR=2,00.
http://www.vasezdravlje.com/izdanje/clanak/158/