Changes of bone histology during maintenance hemodialysis at various levels of dialyzate Ca concentration

The histologic changes in the skeleton of patients on maintenance hemodialysis are well known. However, there are still conflicting reports on whether skeletal lesions progress, remain stationary or regress during treatment by hemodialysis. Under conditions of positive Ca balance, a diminution in the amount of unmineralized osteoid has been observed even without vit D treatment, although a normal process of mineralization with the appearance of a mineralization front has not been seen unless vit D has been administered. On the other hand, a decrease of radioimmunologically measured serum PTH activity has been found, when serum phosphorus was kept in the normal range and dialyzate Ca concentrations in excess of 3.0 mEq/l were used. The purpose of the present study was to examine whether bone histology changes during maintenance hemodialysis and whether the Ca concentration of the dialyzate influences bone histology. Bone histology (iliac crest biopsies; undecalcified sections; micromorphometry) was studied by repeated biopsies in 19 patients on maintenance hemodialysis. The sampling error was assessed by taking 2 biopsies at one time. After an initial biopsy, patients were dialyzed either against 3.6 mEq Ca/l dialyzate or 3.9 mEq Ca/l dialyzate for 9-16 mth before a second biopsy was taken. Bone histology failed to normalize irrespective of the dialyzate Ca concentration. Surface density of endosteal fibrosis diminished in a considerable proportion of the patients (9/19). Volumetric density of osteoid fell in 5 and rose in 4 of the patients.