No correlation between anti-factor Xa levels, low-molecular-weight heparin, and bleeding after gastric bypass

Pulmonary embolism (PE) remains a leading cause of death after Roux-en-Y gastric bypass. Currently, various regimens of low-molecular-weight heparin (LMWH) are used for perioperative deep vein thrombosis (DVT) prophylaxis. Anti-factor Xa (AFXa) has been suggested as a potential marker of LMWH activity. We have developed a perioperative prophylactic DVT regimen for our bariatric patients in which the dosage of LMWH they receive is based on their body mass index (BMI). We looked at whether AFXa levels correlated with bleeding risk.

A retrospective, single institution review of 102 patients undergoing a gastric bypass from November 2003 to April 2004 was performed. Twelve patients received transfusions. AFXa levels were present for 7 of 12 patients requiring transfusions and 74 of 90 patients not requiring transfusions. The average AFXa level for each group was compared.

The transfusion rate for the group was 11.7%, with an average of 2.6 units of blood given (SD 1.2). There was no statistical difference between the average AFXa value for transfused and nontransfused patients (0.13 +/- 0.08 vs. 0.16 +/- 0.19, P = .7).

AFXa levels do not appear to correlate with bleeding risk in patients receiving LMWH prophylaxis following gastric bypass. Determining such risk seems to require another marker.