BACKGROUND: To evaluate a recently introduced blood-saving method for the measurement of activated clotting time (ACT), the Celite i-STAT ACT, by comparing the values obtained with those from the widely used Medtronic ACT II device.
METHODS: In a prospective clinical study, we compared ACT values from the i-STAT device with the Medtronic ACT II device in 60 paediatric, interventional, cardiac catheterization procedures necessitating prophylactic heparinization. Blood samples were pair-analyzed using two i-STAT analyzers and one Medtronic ACT II device with double-tube-cartridges before and after heparinization. Data were compared using Bland-Altman bias analysis, Student's t-test and simple regression analysis.
RESULTS: Bias and precision between the Medtronic ACT II and the i-STAT ACT values was -5.4 +/- 26.3. The i-STAT and Medtronic ACT II values were similar before heparinization (P = 0.22), but i-STAT ACT values became significantly longer than Medtronic ACT II values after heparinization (P = 0.021). The increase of ACT after heparinization was greater (median 86.3; range 40-187 s) in the i-STAT analyzer than in the Medtronic ACT II analyzer (median 73.0; range 19-235.5 s). Increase in ACT values was inversely affected by intraoperative haemoglobin concentration in the Medtronic ACT II analyzer (P = 0.001) but not in the i-STAT analyzer.
CONCLUSION: Activated clotting times obtained from the Celite i-STAT ACT and the Medtronic ACT II demonstrated poor agreement. The technical principles are quite different and the two methods showed diverse susceptibility to intraoperative haemoglobin concentration. Users have to be aware of technique-specific ACT target ranges and their confounders, which need to be provided by the manufacturers.