Determinants of bone loss in patients with Kock ileal urinary reservoir

The purpose of the present study was to determine the change in bone mineral density (BMD) measured with dual energy X-ray absorptiometry (DXA) in patients with Kock reservoirs for urinary diversion who were examined with the same technique 3 years earlier, and relate the changes to kidney function and variables reflecting bone metabolism. A total of 28 patients with Kock ileal reservoirs to the skin (23) or urethra (5) were reinvestigated 3 years after the first measurement. BMD was measured in the lumbar spine, femur and whole body with DXA. Bone specific alkaline phosphatase, osteocalcin, parathyroid hormone (PTH), calcitonin and chloride were also determined in serum. GFR was determined from the plasma clearance of 51Cr-EDTA. The mean values for BMD expressed in percentage of corresponding mean values for age-matched controls (BMD%) were almost identical after 3 years. Only osteocalcin levels correlated with the BMD% values. However, significant positive correlations were found between GFR and the observed individual changes in BMD% over the 3 years in spite of the fact that most GFR values were fairly normal. Enhanced bone loss was associated with high concentrations of osteocalcin and bone specific alkaline phosphatase. Comparisons with blood gas analyses and determination of 1,25 dihydroxyvitamin D performed in the previous study indicate to us that the relation between reduced GFR and low mineral content might, in part, be related to a low-grade metabolic acidosis and reduced availability of the biologically active vitamin D hormone. The conclusion to be drawn is that urinary diversion with a Kock reservoir does not regularly cause bone demineralization. However, patients with even moderately reduced GFR appear to be at risk for developing osteoporosis in the long-time run.