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Basic Laboratory Tests of Hemostatic Function – Prothrombin Time
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Basic Laboratory Tests of Hemostatic Function – Prothrombin Time
The INR component of the laboratory result is a calculated value that is used by the clinician to monitor anticoagulant therapy and adjust dosage as dictated by clinical status.
An INR of 2.0 - 3.0 is often desired as the therapeutic range.
The following formula is used by the clinical laboratory to derive an INR value. The INR must be adjusted for every new lot of PT reagent.
INR= (PT of patient/PT of geometric mean of the normal population)
ISI
The International Sensitivity Index, or ISI value, is provided by the reagent manufacturer as the relative sensitivity of the reagent itself.
The INR is used to standardize PT results, and in turn, anticoagulant therapy, across laboratory instrumentation, methodologies, and locale.
Be sure to frequently check that ISI values match those of the lot currently in use as erroneous results may otherwise occur .
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