Maslow A, et al. - This study was performed on adult cardiac surgical patients, to compare the i-STAT activated clotting time (iACT) to the Hemochron ACT (hACT), both of which were then compared to anti-factor Xa (anti-Xa) assay, a representation of heparin level and activity. iACT and hACT were not equivalent but demonstrated a good association with each other. Overall, the iACT underestimated the hACT. At lower ACTs and anti-Xa levels, there was good agreement between the ACT technologies. This agreement declined with an anti-Xa >0.75 U/mL.