Low molecular weight heparin in hemodialysis and hemofiltration patients. Low molecular weight (LMW)-heparin was used as the sole anticoagulant during hemodialysis and hemofiltration in a pilot study on 32 patients. A LMW-heparin dose corresponding to 50% of the patients usual unfractionated, standard (UF)-heparin dose was found to produce comparable plasma heparin levels (anti-FXa-activity). No thrombosis of the extracorporal system and no bleeding complications occurred at this LMW-heparin dose. In contrast to UF-heparin, LMW-heparin produced only slight increases in PTT and thrombin time in all patients. Lipoprotein lipase was stimulated only marginally by LMW-heparin, with a correspondingly reduced release of free fatty acids. Both heparin species caused similar elevations in factor VIII and fibrin monomers, thus excluding a difference in coagulation activation. On the basis of these results, long-term studies have been started at four nephrology centers. To date, 26 patients have been treated with LMW-heparin for 6 months. A LMW-heparin dose was used that produced plasma anti-FXa-activity of 0.5 to 0.9 U/ml (initial dose: 30 to 40; dose/hr: 8 to 15 anti-FXa-units/kg body wt). PTT and thrombin time were only increased by 5sec on average. Surprisingly, the elevated pre-dialysis levels of factor VIII and fibrin monomers decreased during this 6-month period. Bleeding complications did not occur and thrombotic complications were not observed when the anti-FXa levels were above 0.5 U/ml. LMW-heparin, therefore, appears to be a good alternative to UF-heparin for dialysis patients and may present less risk of bleeding because of its reduced effect on PTT, thrombin time, and thrombocytes.