Content area
Abstract
In a pharmacist-managed anticoagulation clinic, portable point-of-care coagulation devices may facilitate patient monitoring by providing rapid INR measurement. Few studies, however, have validated this type of device.
To evaluate the reliability, validity and ease of use of the CoaguChek S, a new portable coagulation device.
A total of 100 patients followed at a pharmacist-managed anticoagulation clinic attended two study visits. INRs were measured using the CoaguChek S and the standard laboratory technique.
Reliability: The test-retest reliability (precision) of the CoaguChek S, estimated by the intraclass correlation coefficient (ICC) and a 95% confidence interval (95% CI), was high (0.98 (0.98-0.99)) and comparable to the standard laboratory technique (0.99 (0.98-0.99)). Interrater reliability was also high (0.97 (0.95-0.98)). Reliability coefficients did not vary with the test-strip lot number nor the CoaguChek S operator.
When compared with standard laboratory procedure, the ICC (95% CI) was equal to 0.93 (0.91-0.95). The mean difference (95% CI) between INR measured by the laboratory and the CoaguChek S was equal to -0.02 units (-0.06-0.03). The mean absolute and relative absolute differences (95% CI) were equal to 0.24 units (0.21-0.27) and 9% (8%-10%), respectively. Differences tended to increase for INRs greater than 3 units as seen by a mean difference (95% CI) of -0.17 units (-0.35-0.02). This represented a mean absolute difference (95% CI) of 0.44 units (0.33-0.55) and a mean relative absolute difference of 12% (9%-15%). Concordance between therapeutic decisions based on CoaguChek S and laboratory results was high (Kappa = 0.68). In 34 cases (18%), the therapeutic decision would have been different. However, in 15 of these discordant observations, the difference between the CoaguCheck S and laboratory INR was <or=0.25 units. Ease of use: In 3% of cases, no INR could be measured by the CoaguChek S. The percentage of extra finger pricks and extra test-strips were equal to 25.8% and 23.7%, respectively.
When used by health professionals in a pharmacist-managed anticoagulation clinic, the CoaguChek S is reliable, valid and easy to use. However, its validity tends to decrease as the INR increases, possibly due to the low sensitivity of the thromboplastin. If the CoaguChek S INR is supratherapeutic, we would therefore recommend confirming the results with a standard laboratory measurement.