Summary
Whole-blood point-of-care testing prothrombin time monitors are being used on an increasing
scale for the monitoring of oral anticoagulant therapy. These monitors are used with
disposable test strips containing tissue factor reagent. The purpose of the present
study was to assess the stability of different Coagu-Chek-S strip lots for a period
of one year. Ten strip lots introduced successively in the Netherlands were obtained
from the manufacturer's representative and stored at 4–8°C. Six deep-frozen pooled
plasmas were analyzed for the prothrombin time and INR with the strips at six or seven
occasions spread over one year. The test plasmas were recalcified immediately before
application to the Coagu Chek-S system. Regression analysis was performed on the clotting
times obtained with each plasma. In the majority of cases (i.e. 95%), no significant
change was observed at the 5% significance level. A significant change was observed
in only 3 cases. In addition, a ranking statistic was used as test of a monotonic
relationship in the two-way analysis of variance. The results of the ranking statistic
were not significant for any strip lot, indicating that the test strips were stable
under these storage conditions. The reproducibility of INR measured with the Coagu
Chek-S was assessed. The mean within-run coefficient of variation (CV) of INR ranged
from 2.58% to 3.36% (CV). The between-lot variation of the mean INR ranged from 3.2
to 4.5 % (CV). The over-all variation of single INR measurements, i.e. including between-lot
and within-lot, ranged from 5.0 to 6.0 % (CV).
Keywords
Point-of-care testing - oral anticoagulant therapy - prothrombin time - INR - quality
control
