Hyperphosphatemia is consistently associated with increased all-cause and cardiovascular mortality in maintenance hemodialysis (MHD) patients across all age categories, researchers reported in the Journal of Renal Nutrition (2013;23:411-421). Hypophosphatemia is associated with increased all-cause mortality only in elderly patients.
A team led by Kamyar Kalantar-Zadeh, MD, MPH, PhD, of the University of California Irvine, analyzed data from a six-year cohort of 107,817 MHD patients, whom they divided into five age categories: 15 years and older, but younger than 45; 45 and older, but younger than 65; 65 and older but younger than 70; 70 and older, but younger than 75; and 75 and older. The mean time-average phosphorus levels for these categories were 6.26, 5.65, 5.26, 5.11, and 4.88 mg/dL, respectively. The researchers defined hyperphosphatemia as a phosphorus level greater than 5.5 mg/dL and hypophosphatemia as a level below 3.5 mg/dL.
Compared with a phosphorus level of 3.5-5.5, levels higher than 5.5 but not more than 6.5 were associated with a 9%, 11%, 11%, 13%, and 16% increased risk of all-cause mortality, respectively, and an 18%, 22%, 16%, 12% and 23% increased risk of cardiovascular mortality, respectively, in adjusted analyses. Levels higher than 6.5 but not more than 7.5 were associated with a 26%, 36%, 49%, 41%, and 34% increased risk of all-cause mortality and 37%, 49%, 67%, 50%, and 42%, increased risk of cardiovascular mortality.
The study also showed that hypophosphatemia was associated with a significant 21%, 13%, and 28% increased risk of all-cause mortality among patients 65 and older, but younger than 70, 70 and older, but younger than 75, and 75 and older, respectively. Hypophosphatemia was associated with a significant 26% and 32% increased risk of cardiovascular mortality among patients 65 and older, but younger than 70 and those 75 and older, respectively.
Hypophosphatemia was not significantly associated with all-cause and cardiovascular mortality among patients younger than 65.
“Preventing very low serum phosphorus levels in elderly dialysis patients (for instance, by liberalizing dietary protein intake) may be associated with better outcomes,” the authors noted.