Evaluation of activated partial thromboplastin time (aPTT) reagents for application in biomedical diagnostic device development.

INTRODUCTION The most commonly used test for monitoring heparin therapy is the activated partial thromboplastin time (aPTT). The response of available aPTT reagents to heparin varies significantly. The aim of this study was to highlight the differences between aPTT reagents stored in a dried format to select the most suitable formulations to be used for the development of point-of-care diagnostic devices used for monitoring of unfractionated heparin dose response. METHODS Ten reagents were analysed in terms of their performance in liquid and in dried form after storage for 24 h and 14 days. Performance was assessed by measurement of the clotting time (CT) as evidenced by the onset of thrombin formation using a chromogenic thrombin substrate in plasma samples activated with these formulations. RESULTS Reagents in all of the three forms tested (liquid, 24 h and 14 days) resulted in significant shortening of CTs in comparison with the nonactivated plasma CT. Liquids returned more rapid CTs in comparison with dried reagents. Most of the reagents were more sensitive to heparin in dried, rather than in liquid form. Dried reagents based on kaolin as a surface activator were notably more effective in achieving short CT than others, while dried reagents composed of silica and synthetic phospholipids were the most sensitive to heparin. CONCLUSION Two reagents, namely aPTT-SP and SynthASIL both of which are based on synthetic phospholipids and silica, were identified as promising candidates for incorporation into point-of-care diagnostic device platforms as dried reagents.