Validation of the CoaguChek XS international normalised ratio point-of-care analyser in patients at Charlotte Maxeke Johannesburg Academic Hospital, South Africa.

BACKGROUND Measurement of the international normalised ratio (INR) is essential in the management of patients on long-term warfarin therapy. The CoaguChek XS portable coagulometer is a point-of-care test for INR measurement. It offers the advantage of improved patient accessibility, particularly in peripheral clinics. OBJECTIVES To evaluate the clinical utility of the CoaguChek XS for monitoring of patients on standard warfarin therapy (INR 2 - 3) as well as those with mechanical heart valve replacements (INR 2.5 - 3.5). METHODS We compared the performance of the CoaguChek XS device with that of the STAGO laboratory analyser with regard to accuracy and precision in 304 patients referred for routine testing. RESULTS The mean INR value of the CoaguChek XS of 2.75 (standard deviation (SD) 1.18) was comparable to that of the STAGO (2.65 (SD 1.04)). The Bland-Altman difference plot revealed good agreement. Bias between the two methods was small, and the imprecision was within acceptable limits. Within the target range (2.0 - 3.5), 93.9% of the CoaguChek XS INR readings were within 0.5 units of the standard laboratory method result. There was, however, an increase in the variability of the differences between the two test methods when the INR was >3.6. CONCLUSION The CoaguChek XS point-of-care device can be used to provide accurate and precise INR measurements over a wide range for monitoring of valvular and non-valvular patients on long-term warfarin therapy.