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Arch Pathol Lab Med. 1998 Nov;122(11):972-7.

Use of different thromboplastin reagents causes greater variability in international normalized ratio results than prolonged room temperature storage of specimens.

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  • 1Special Hematology Laboratory, Gundersen Clinic Ltd, LaCrosse, Wis, USA.



To determine whether a 24-hour delay in testing affects international normalized ratio (INR) reproducibility as much as using alternative thromboplastin reagents.


Specimens from warfarin-treated patients were tested at 0 hours and again at 24 hours to determine the INR, each time using RecombiPlasTin, Innovin, and C-Plus thromboplastin reagents.


There was no clinically significant difference in INRs when a specimen was tested with the same reagent at 0 and 24 hours. However, at 0 hours, the INRs were significantly higher when a specimen was tested using C-Plus and RecombiPlasTin as compared with the result with Innovin (both P < .0001).


A specimen can be maintained at room temperature for 24 hours without a significant change in the INR. Changing the reagent, however, can result in statistically and clinically significant differences in the INR.

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