Laboratory reporting of the international normalized ratio: progress and problems.
BACKGROUND
The international normalized ratio (INR) is widely used to monitor oral anticoagulation and to evaluate patients with coagulation disorders.


OBJECTIVE
To examine the variability of the performance and reporting of the INR and to evaluate laboratory calculation of the INR.


METHODS
Between 1993 and 2003, laboratories participating in proficiency testing were surveyed. Participants provided the international sensitivity index and the mean normal prothrombin time used to calculate the INR. The INR was calculated from the data provided and compared with the INR reported to determine if the calculation was correct.


RESULTS
Survey data regarding the INR collected between 1993 and 2003 demonstrate an improvement in reporting, using appropriate anticoagulant, using lower international sensitivity index reagents, and matching international sensitivity index and prothrombin time method. The all-method coefficient of variation of the INR improved from 18% to 5.8%. Among 3813 laboratories studied in 2002 and 2003, 4.1% miscalculated INR. Of 29 laboratories that reported investigation of the INR miscalculation, 11 (38%) reported correcting an INR that was being reported in patient results and that this error was corrected as a result of the study. Since beginning grading of the INR calculation, miscalculation of the INR has fallen to less than 1%.


CONCLUSIONS
Recommendations for change in laboratory practice made by consensus conferences are implemented during the course of many years. Difficulty calculating the INR was documented, and both the calculation and the variability in the reporting of the INR showed improvement. Proficiency testing, when closely evaluated and acted on, can have a direct impact on the quality of patient care.
Olson
John D
JD
Department of Pathology, University of Texas Health Science Center, San Antonio, TX 78229-3900, USA. olsonj@uthscsa.edu
Brandt
John T
JT
Chandler
Wayne L
WL
Van Cott
Elizabeth M
EM
Cunningham
Mark T
MT
Hayes
Timothy E
TE
Kottke-Marchant
Kandice K
KK
Makar
Robert S
RS
Uy
Arby B
AB
Wang
Edward C
EC
D000925:Anticoagulants / Q000009:adverse effects / Q000627:therapeutic use; D001778:Blood Coagulation Disorders / Q000175:diagnosis; D019411:Clinical Laboratory Techniques / Q000592:standards*; D003625:Data Collection / Q000592:standards; D019538:Health Care Surveys; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods* / Q000592:standards; D008137:Longitudinal Studies; D017056:Medical Laboratory Personnel / Q000193:education; D010337:Pathology Department, Hospital / Q000592:standards*; D011361:Professional Competence; D011517:Prothrombin Time / Q000379:methods / Q000592:standards; D011787:Quality of Health Care / Q000639:trends; D012680:Sensitivity and Specificity
D000925:Anticoagulants