Use of different thromboplastin reagents causes greater variability in international normalized ratio results than prolonged room temperature storage of specimens.
OBJECTIVE
To determine whether a 24-hour delay in testing affects international normalized ratio (INR) reproducibility as much as using alternative thromboplastin reagents.


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Davis
K D
KD
Special Hematology Laboratory, Gundersen Clinic Ltd, LaCrosse, Wis, USA.
Danielson
C F
CF
May
L S
LS
Han
Z Q
ZQ
D000925:Anticoagulants / Q000627:therapeutic use; D001793:Blood Preservation; D006801:Humans; D007202:Indicators and Reagents; D019934:International Normalized Ratio / Q000592:standards*; D010314:Partial Thromboplastin Time; D013696:Temperature; D013925:Thromboplastin / Q000592:standards*; D014859:Warfarin / Q000627:therapeutic use
D000925:Anticoagulants; D007202:Indicators and Reagents; D014859:Warfarin; D013925:Thromboplastin