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Activated clotting time (ACT) testing: analysis of reproducibility
M L Zucker1, C Jobes, M Siegel
1International Technidyne Corporation, Edison, NJ 08820, USA.
Insights
Activated Clotting Time (ACT) tests demonstrate precision well below the 10% CV standard. This study confirms Hemochron ACT test tubes offer reliable heparin monitoring in cardiac surgery, using both lab and clinical data.
Area of Science:
- Cardiovascular Surgery
- Hematology
- Medical Device Evaluation
Background:
- Activated Clotting Time (ACT) is the standard for heparin monitoring in cardiac surgery.
- Current precision standards (10% CV) may not reflect modern test performance.
- Recent precision data for ACT testing is limited.
Purpose of the Study:
- To evaluate the precision of Hemochron FTCA510 (celite) and KACT (kaolin) ACT test tubes.
- To determine if ACT test variability meets or exceeds the 10% CV standard.
- To assess ACT test reliability in laboratory and clinical settings.
Main Methods:
- Retrospective analysis of laboratory and clinical data for Hemochron ACT tests.
- Evaluation of reproducibility using multiple lots of control plasma and fresh heparinized blood.
- Analysis of coefficient of variation (CV) across various heparin concentrations and clinical samples.
Main Results:
- Both celite and kaolin ACT tests showed average CVs significantly below 10% in laboratory studies (e.g., celite 5.4% normal, 4.0% abnormal; kaolin 4.5% normal, 3.8% abnormal).
- Precision was even higher with fresh whole blood compared to control plasma.
- Clinical evaluation demonstrated minimal differences in paired ACT values (average 1.8% difference).
Conclusions:
- Hemochron ACT test tubes (celite and kaolin) exhibit precision significantly better than the 10% CV standard.
- These ACT tests provide reliable heparin anticoagulation monitoring for cardiac surgery.
- The study validates the accuracy and consistency of Hemochron ACT testing in real-world clinical use.
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 range 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%.