ObjectivesAccording to the manufacturer, the Hemochron ACT-LR cuvette is designated for heparin concentrations of 0-2.5 IU/ml while the optimal concentration range for the ACT+ cartridge is 1-6 IU/ml. We hypothesized that at low to moderate heparin concentrations, ACT-LR is more reliable than ACT+. DesignAn in vitro study SettingA tertiary care university hospital ParticipantsTwenty healthy adult volunteers. InterventionsDonor blood samples were spiked with unfractionated heparin to concentrations of 0, 0.5, 1.0, 1.5, 2.0 and 2.5 IU/ml. From each concentration, three measurements were conducted with each test cassette using three different Hemochron Signature Elite devices, totaling 720 ACT tests. The Bland-Altman method and intraclass correlation coefficients were used to analyze the data. Measurements and Main ResultsAll 360 ACT+ tests yielded a result. Instead, 38/360 (11%) ACT-LR tests ran above the upper measurement range; of these, 36 were from the 120 measurements at heparin concentrations ≥ 2.0 IU/ml. The bias between all ACT-LR and ACT+ measurements was 52 (95% CI, 48 to 56) celite seconds, and the limits of agreement were wide. Based on the intraclass correlation coefficients, the reliability of ACT+ was better than or equal to that of ACT-LR. ConclusionsThe performance of ACT+ is equal to that of ACT-LR up to concentration of 0.5 IU/ml, above which ACT+ is superior to ACT-LR, questioning the rationale for a specific low-range test. However, there is a significant bias between ACT-LR and ACT+ measurements that needs to be considered if switching from one test to the other.
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