The Use of Point of Care Testing for Monitoring of APTT in Patients Receiving Heparin Infusion

Background: There is a high risk of thromboembolic events among patients undergoing cardiac surgery, and perioperative anticoagulation is sometimes required. The time taken for laboratory based APTT blood sampling results and adjustments may compromise patient safety. There is evidence in the literature to suggest that bedside testing turnaround times is of benefit to inpatient care, and conversely that POCT is inaccurate. The primary aim of this study was to determine if point of care testing of APTT was accurate when compared to laboratory based APTT measurements. The secondary aim was to identify if there was a correlation between operator experience and accuracy of results.

Methods: Following full ethics approval by the Royal Adelaide Hospital, Human Research Ethics Committee (HREC), current Cardiothoracic Surgery Unit inpatients were enrolled in the study over a period from July 2016-March 2017. A total of 50 samples were obtained from the minimum number of patients required and separated into three tiers; point of care testing group from finger prick test, point of care testing group from standard postoperative blood sample, and laboratory based testing of standard postoperative blood sample. Results were correlated with Central Adelaide Local Health Network (CALHN) heparin infusion protocols. Clinically significant samples were those which POCT IV and laboratory IV results varied enough to alter the heparin infusion protocol rate change.

Results: Demographics showed 83% of patients were male, 67% were receiving IV heparin preoperatively for unstable coronary artery disease, and the mean age of participants was 66 years. Of the 50 collected samples, 17/50 (34%) were recorded as being clinically significant. On the adjusted POCT protocol, 14/50 (28%) of samples were clinically significant. There was a statistically significant difference between POCT IV and laboratory IV results; p = 0.02 and mean difference between values was 19.1. Linear regression analysis showed a poor correlation between POCT IV and laboratory IV samples. There was no relationship between preoperative and postoperative samples. Conclusions: Point of care testing in our study of 50 patient samples shows that there is a poor correlation between POCT and laboratory based testing. Additionally, there is a steep learning curve for those performing the test with no marked improvement following progressive samples. Accordingly, POCT testing in cardiac surgery patients is not recommended for clinical use until further research is completed showing improved correlation between tests, and methods to overcome the steep learning curve are identified.