inr
Table of Contents
INR
see also:
introduction
- the International Normalised Ratio or INR test measures the overall activity of the extrinsic coagulation pathway.
- performed by adding thromboplastin to an aliquot of the patient's plasma
- length of time taken for the mixture to clot is called the prothrombin time.
- the same test is performed using a normal control plasma and the prothrombin ratio is the derived by dividing the patient clotting time by the control clotting time.
- finally, the INR is calculated using the 'international sensitivity index' of the thromboplastin reagent so that the ratio obtained is independent of the reagent brand or the testing laboratory.
- normal range for INR is 1.0-1.3
- usual target therapeutic INR for warfarin Rx are:
- prosthetic heart valves: 2.5-3.5
causes of a prolonged INR
- deficiency of one or more coagulation factors in the extrinsic coagulation pathway
- this may be caused by either:
- warfarin Rx
- malnutrition
- impaired liver function
- other causes
- presence of a lupus type coagulation inhibitor - an in vitro phenomenon giving falsely prolonged results in some patients.
- presence of heparin (but not LMW heparin)
inr.txt · Last modified: 2009/09/01 05:03 by 127.0.0.1