THE DETERMINATION OF INR IN STORED WHOLE-BLOOD

Aims-To examine the reliability of international normalised ratio (INR ) determination on samples stored as whole blood for up to two days at room temperature. Methods-The INR of 40 patients receiving oral antic oagulants was determined on fresh blood and on samples stored far 24 a nd 48 hours, using five locally calibrated prothrombin time systems. T hese incorporated Manchester reagent, Recombiplastin, IL PT Fibrinogen HS Plus, Manchester combined capillary prothrombin rime reagent, and a freeze dried in-house reference rabbit brain thromboplastin, RBT 101 0. In addition, factors II, V,VII, and X mere determined on samples ob tained from 18 of these patients before and after incubation at room t emperature. Results-The INR of the samples changed by differing amount s during storage, depending on which system was employed. Although the mean change after 24 hours storage was relatively small, there were i ndividual samples that changed by > 0.5 LNR with all systems. These ch anges mould lead to adjustment in dosage of certain patients. After 48 hours these effects were greater with all systems except that employi ng Recombiplastin. There were only small reductions in the measured fa ctors by 48 hours. Conclusions-After storage of samples for only 24 ho urs, some patients' INR changed sufficiently to affect dosage, In view of these observations, the practice of storing whole blood samples fo r INR determination cannot be recommended.