Plasma heparin levels after low dose subcutaneous heparin in patients undergoing hip replacement

Plasma heparin levels were measured at 2 and 8 h after 5000 iu of heparin subcutaneously in 43 patients awaiting total hip replacement. At 2 h, 37 patients had plasma levels between 0.05 and 0.15 iu/ml, three patients had more than 0.2 iu/ml, and three had only trace levels. At 8 h, most patients had less than 0.1 iu/ml, and six patients had no detectable plasma heparin. There were no correlations between plasma heparin levels and age, sex, body weight or use of analgesics. Patients with high 2 h plasma heparin levels may bleed at operation, whereas those with very low plasma heparin concentrations may be at risk of post-operative venous thrombosis; it may therefore sometimes be necessary to monitor plasma heparin levels in order to determine the optimal regime in individual cases.