Performance of Hemochron ACT-LR and ACT+ Test Cuvettes in Monitoring Low to Moderate Heparin Concentrations: An In Vitro Study

According to the manufacturer, the Hemochron ACT-LR cuvette is designated for heparin concentrations of 0 to 2.5 IU/mL, while the optimal concentration range for the ACT+ cartridge is 1 to 6 IU/mL. We hypothesized that at low to moderate heparin concentrations, the ACT-LR is more reliable than the ACT+. An in vitro study. A tertiary care university hospital. Twenty healthy adult volunteers. Donor 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, 3 measurements were made with each test cassette using 3 different Hemochron Signature Elite devices, for a total of 720 ACT tests. The Bland-Altman method and intraclass correlation coefficients were used to analyze the data. All 360 ACT+ tests yielded a result. Of 360, 38 (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, 48-56) 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. The performance of ACT+ is equal to that of ACT-LR up to a 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.