The influence of sampling technique on ACT Plus results

The manufacturer of the ACT Plus Automated Coagulation Timer, Medtronic Inc., recommends that test cartridges be prewarmed and the activating reagent resuspended (tapped/ mixed) before patient testing. In a busy clinical environment, these recommendations may be overlooked or disregarded. In this study, the impact of sampling technique on ACT Plus test results was investigated. In Series 1, two test cartridges were split into four individual chambers. Two ACT Plus machines were used, allowing for three separate comparisons to be made. The sample results from test Chambers 2 (cold/tapped), 3 (warmed/ not tapped), and 4 (cold/not tapped) were compared individually against the result from test Chamber 1, the recommended technique (warm/tapped). In Series 2, the manufacturer's recommendations were tested using a single double cartridge (warm/ tapped). Results were interpreted using the Bland-Altman method of analysis. The prewarming and tapping of cartridges before use independently influenced the agreement of results when compared with cartridges that were not prewarmed and tapped. Each factor (temperature and mixing) when excluded was found to affect the standard deviation and decrease the agreement of results. By following the manufacturer's recommendations to standardize the sampling technique, ACT Plus test results are more accurate.