Mild Hyperphosphatemia and Mortality in Hemodialysis Patients

Background: Severe hyperphosphatemia (serum phosphate level > 6.5 mg/dL [>2.10 mmol/L]) has been associated directly with increased overall and cardiovascular mortality in hemodialysis (HD) patients. Currently, clinical guidelines recommend maintaining phosphate levels within normal range (3.0 to 5.0 mg/dL [0.97 to 1.61 mmol/L]). However, mild hyperphosphatemia (phosphate, 5.01 to 6.5 mg/dL [1.62 to 2.10 mmol/L]) is still to be addressed as an independent mortality risk factor in HD patients. Methods: The association between serum phosphate level and survival in maintenance HD patients was explored prospectively in 385 incident patients from 1990 to 2001. Cox regression was performed using phosphate level as: (1) a continuous variable; (2) stratified as low phosphate level (<3 mg/dL [<0.97 mmol/L]), normal phosphate level (3.0 to 5.0 mg/dL [0.97 to 1.61 mmol/L]), mild hyperphosphatemia (phosphate, 5.01 to 6.5 mg/dL [1.62 to 2.10 mmol/L]), or severe hyperphosphatemia (phosphate > 6.5 mg/dL [>2.10 mmol/L]); and (3) phosphate level greater or less than 5.0 mg/dL (> or <1.61 mmol/L). Results: As a continuous variable, relative risk (RR) for mortality for serum phosphate level was 1.26 (confidence interval [CI], 1.09 to 1.47) after adjusting for age, sex, diabetes, Kt/V, albumin level, hemoglobin level, serum calcium level, normalized protein catabolic rate, and parathyroid hormone level. Compared with a normal phosphate level, mild hyperphosphatemia showed an adjusted mortality RR of 1.94 (CI, 1.17 to 3.19), and severe hyperphosphatemia, an RR of 2.02 (CI, 1.10 to 3.73). Patients with a phosphate level cutoff value greater than 5.0 mg/dL (>1.61 mmol/L) showed a 2-fold increase in adjusted RR for mortality compared with those with a phosphate level of 5.0 mg/dL or less (≤1.61 mmol/L; RR, 2.11; CI, 1.44 to 3.08). Conclusion: A serum phosphate level greater than 5.0 mg/dL (>1.61 mmol/L) is independently associated with an increased risk for death in HD patients.