ULTRADIAN VARIATION IN SERUM PHOSPHATE CONCENTRATION IN PATIENTS ON HEMODIALYSIS

To study how much the serum phosphate concentration could vary on the day before scheduled dialysis we obtained 24-37 timed measurements dur ing 24 h in nine patients on maintenance haemodialysis. During the obs ervation there was an increase in serum phosphate concentration of 0.2 39 +/- 0.022, P<0.01). Surprisingly six of the nine patients exhibited nine statistically and clinically significant nadirs with decrements of 0.21 +/- 0.04 mmol/l against an intra-assay standard deviation of a bout 0.05 mmol/l. Five of the nadirs occurred at 11.40-14.50, mean 12. 59, and three at 19.00-21.30, mean 20.00. We found no coinciding chang es in the serum calcium concentration. These findings indicate that se rum phosphate concentrations do not always reflect phosphorus balance or intake.