Activated Clotting Time (ACT) Testing: Analysis of Reproducibility

Abstract

Activated Clotting Time (ACT) has been the standard for monitoring heparin anticoagulation in cardiac surgery for three decades. Although a 10% coefficient of variation (CV) is the referenced standard for the test, no recent reports of precision are available. The precision of Hemochron FTCA510 (celite) and KACT (kaolin) ACT test tubes was evaluated using a retrospective analysis of results from both laboratory studies and routine clinical usage. Laboratory studies of reproducibility included analysis of the CV from repetitive testing using multiple lots of ACTs. Substrates used included 40 consecutive lots of control plasma and freshly heparinized donor blood. Across the lots of control plasma, the celite ACT yielded an average CV of 5.4% for the normal control level and 4.0% in the abnormal control level (range 3.6–9.7% and 2.7–6.3%, respectively). The KACT showed similar performance for the normal (mean = 4.5%, range 2.2–7.8%) and abnormal (mean = 3.8%, range 2.0–10.0%). These values, significantly less than 10%, reflect the combined variability of both the ACT tests and the lyophilized, single use vial, control material. Fresh whole blood samples exhibited improved ACT precision when compared to this artificial substrate. CVs for the celite ACT ranged from 0.6–6.0% at one unit heparin/ml blood to 2.4–11.6% at 5 units/ml where clotting times exceed 650 sec. The KACT showed even lower CVs at all heparin levels, with values of 2.4–7.0%. Clinical evaluations included samples (N = 56) collected from cardiac surgery patients with celite ACT values ranging to 744 sec. Duplicate values differed by an average of 7.5 sec or 1.8%. There was only one clinically significant difference in paired values; a 376 sec paired with a 406 sec, 400 sec being the clinical target time. This retrospective data analysis demonstrates that Hemochron ACT variability is significantly less than 10%.

Evaluations of Activated Clotting Time Technologies Require Understanding Activating Clotting Time System Differences

“…2012;44:15-20), presented an interesting in vitro comparison of four different systems for measuring the activated clotting time (ACT) test. The results of this evaluation confirmed earlier studies in demonstrating that no two ACT test systems report the same results on a given blood sample, the clear message being that there is no standardization in ACT testing (1)(2)(3)(4)(5).…”

“…Accuracy can only be evaluated when there is a "true" value to which all systems can be compared, ease of use was omitted from the results and discussion of the arti-cle, and cost was listed only in a table in the appendix. Reproducibility was the only parameter evaluated and all four systems revealed performance (coefficient of variation <10%) well within the general expectations for ACT test precision (3,6). The observed differences in reproducibility (coefficient of variation range 3.3-7.1%) would have no effect on clinical decisions to increase or decrease heparin dosing, even for extremely low-range heparin anticoagulation such as patients on continuous heparin infusion for thromboembolic therapy.…”

Validation of a New Whole Blood Coagulation Monitoring System

“…The CVs between two different operators were less than 5% (Tables 1 and 2). In a previous study using the Hemochron (standard) ACT, two independent operators obtained CVs in the 4-5% range (8). Increases in variability outside of the clinical setting are expected because of the dependence of this system on operator technique (9).…”