Discordant Partial Thromboplastin Time (PTT) vs Anti-Xa Heparin Activity

To determine the relationship between baseline variations in the partial thromboplastin time (PTT) and the discordance between the PTT and anti-Xa heparin activity (anti-Xa) during heparin therapy.

The baseline PTT on heparin was determined using automated heparin neutralization with protamine (prPTT). The prPTT was used to calculate a baseline-corrected PTT on heparin to reduce discordance with anti-Xa measurements.

The prPTT removed up to 1 U/mL of heparin, returning baseline values for normal, factor-deficient, and lupus inhibitor plasmas. A prolonged prPTT was seen in 97 (53%) of 182 samples from heparinized patients. The heparinized PTT was discordant compared with anti-Xa in 64 (35%) of 182 samples and 43 (67%) of 64 discordant samples, and 46% of concordant samples showed a prolonged prPTT. A baseline-corrected PTT reduced discordance with anti-Xa measurements by 64%.

PTT/anti-Xa discordance due to baseline PTT prolongation could be reduced using a baseline-corrected PTT.