Serum LDH and LDH isoenzymes in chronic renal failure: effect of hemodialysis.

Serum levels of several commonly measured enzymes are abnormal in patients with end-stage renal disease (ESRD). In the present study we measured serum total LDH activity and LDH isoenzymes in a group of 25 ESRD patients shortly before, during, and immediately after hemodialysis. Baseline serum total LDH activity in the ESRD group was midly but significantly higher than that found in the normal control group. The observed elevation was associated with an isomorphic pattern. Single passage of blood through the extracorporeal apparatus led to a rise in total LDH, LDH-3, LDH-2 and LDH-4, a pattern consistent with release from the platelets. A steady increase was noted in total LDH, LDH-5 and LDH-1 of arterial blood during hemodialysis. This was thought to be due to ultrafiltration-induced hemoconcentration, enzyme release from the formed elements within the extracorporeal circuit and complement-mediated leukocyte activation and pulmonary leukostasis. These observations should be taken into consideration with regards to interpretation of LDH and LDH isoenzyme values and proper time of blood sampling in ESRD patients.