Measurement of activated clotting time in children -: comparison of the Celite i-STAT® ACT with the Medtronic ACT® II

Background: To evaluate a recently introduced blood-saving method for the measurement of activated clotting time (ACT), the Celite i-STAT((R)) ACT, by comparing the values obtained with those from the widely used Medtronic ACT((R)) II device. Methods: In a prospective clinical study, we compared ACT values from the i-STAT((R)) device with the Medtronic ACT((R)) II device in 60 paediatric, interventional, cardiac catheterization procedures necessitating prophylactic heparinization. Blood samples were pair-analyzed using two i-STAT((R)) analyzers and one Medtronic ACT((R)) 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((R)) II and the i-STAT((R)) ACT values was -5.4 +/- 26.3. The i-STAT((R)) and Medtronic ACT((R)) II values were similar before heparinization (P = 0.22), but i-STAT((R)) ACT values became significantly longer than Medtronic ACT((R)) 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((R)) analyzer than in the Medtronic ACT((R)) 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((R)) II analyzer (P = 0.001) but not in the i-STAT((R)) analyzer. Conclusion: Activated clotting times obtained from the Celite i-STAT((R)) ACT and the Medtronic ACT((R)) 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.