Background: Hyperphosphatemia is an independent risk factor for mortality in hemodialysis (HD) patients. The relative importance of HD frequency and duration for phosphate removal is not clear. Short daily hemodialysis (SDHD) is a form of HD which offers increased treatment frequency. SDHD studies have not been shown to normalize serum phosphate.
Methods: Twenty-one patients were converted from conventional thrice weekly HD (CHD, 4 h/session) to SDHD (2 - 3.75 h/session, 5 - 6 sessions per week). The primary endpoint was the change in predialysis serum phosphate levels after conversion from CHD to SDHD. Changes in serum calcium levels, phosphate binder and vitamin D analogue usage, and serum parathyroid hormone (PTH) levels were measured as secondary endpoints.
Results: Mean duration of SDHD was 17.7 +/- 1.9 months. Mean treatment time was 2.63 +/- 0.10 h, and mean frequency was 5.3 +/- 0.1 sessions per week. Predialysis serum phosphate decreased from 1.99 +/- 0.12 mM at three months pre conversion to 1.27 +/- 0.10 mM at six months post conversion to SDHD (p = 0.002). Serum phosphate remained stable between six and 12 months post conversion (1.27 +/- 0.10 mM to 1.38 +/- 0.14 mM, p = 0.8). When patients were grouped according to SDHD sessional frequency (five sessions/week versus six sessions/week) and compared, no significant differences were found in predialysis serum phosphate levels at six or 12 months post conversion. There were no changes in serum calcium. Overall phosphate binder usage did not change pre and post conversion to SDHD. Serum PTH tended to decrease after one year of SDHD (44.2 +/- 13.4 pM to 21.4 +/- 5.9 pM, p = 0.07).
Conclusion: Conversion to SDHD significantly decreased serum phosphate. There may be a minimum hemodialysis duration below which increases in frequency are not able to compensate to achieve normal phosphate levels. Future studies are necessary to better characterize the relationship between HD duration and frequency with respect to phosphate removal.