In vitro evidence of gender-related heparin resistance.

Coagulability varies among men, women, and pregnant women, along a spectrum where the blood of men is the least and that of pregnant women the most coagulable. The effects of differences in coagulation status on the action of heparin cannot be measured by specific laboratory tests such as aPTT or anti-Factor Xa assay. Thromboelastography which measures whole blood coagulation can assess the effect of heparin against differing backgrounds of coagulation. The aim of this in vitro study was to explore differences in heparin effect between men, women and pregnant women. Fifteen male and female staff volunteers, and 15 pregnant women approaching term, donated venous blood, which was added to four cups in two TEG 5000 analysers. In the cups of the analysers was 0.03 mL of saline control, or heparin 0.4, 0.6 or 1 unit/mL. TEG variables r and k, angle and MA were compared across the groups using two way ANOVA. All subject groups demonstrated a significant heparin effect, which was least in the control group and greatest with 1 unit/mL (P < 0.0001). Across the subject groups, from men to pregnant women, increasing coagulability was seen, with shortening of r and k (P < 0.04), and increasing angle and MA (P < 0.0001). A relationship between gender and heparin was significant for r and k (P < 0.02) but not for angle and MA. This result assists the case against a one-size-fits-all approach to policies on heparinisation.