Modified Microsample ACT Test for Heparin Monitoring

The activated clotting time (ACT) is a standard method of heparin monitoring during cardiac angioplasty and cardiac surgery. A modified ACT (ACT+) which employs a microsample blood volume (0.05 ml) and yields faster clotting time results than a conventional Hemochron ACT was evaluated and compared to the standard ACT. The ACT+, determined using a single channel general purpose analyzer (Hemochron Jr.), employs a plastic cuvette containing dried ACT reagents (kaolin-silica-phospholipid). In vitro evaluation of heparinized normal donor blood demonstrated the test insensitivity to aprotinin. Using split blood specimens, duplicate ACT and ACT+ were performed (n=92) and a correlation between the two was established. In evaluation of 79 cardiac surgery and 53 angioplasty patients, good correlation was observed between ACT+ and Hemochron ACT (r=0.93, n=574). Mean versus difference plots demonstrated an improved reproducibility of the ACT+ (Mean SD=35 seconds) compared to the ACT (Mean SD=53 seconds), presumably due to automation of the blood sample sizing and blood/reagent mixing. These studies indicate that the microsample ACT+ is an alternative to the conventional ACT with an advantage of small sample requirement and rapid reproducible results.