Relationships Between Serum and Urine Phosphorus With All-Cause and Cardiovascular Mortality: The Osteoporotic Fractures in Men (MrOS) Study

Background: Serum phosphorus is associated with cardiovascular disease (CVD) in the general population, but may not comprehensively reflect phosphorus homeostasis. Whether urine phosphorus-creatinine ratio (a marker of intestinal absorption) or urine fractional excretion of phosphorus (FE; a marker of urinary phosphorus handling) is associated with risk of mortality or CVD is uncertain. Study Design: Prospective observational study. Setting & Participants: 1,325 community-dwelling men 65 years or older participating in the MrOS Study. Predictor: Serum phosphorus, urine phosphorus-creatinine ratio, and Outcomes: All-cause and CVD death. Results: Mean age was 74 +/- 6 (SD) years, estimated glomerular filtration rate was 75 16 mL/min/1.73 m(2), and serum phosphorus level was 3.2 +/- 0.4 mg/dL. During a median follow-up of 9.3 years, there were 364 (120 CVD) deaths. After adjustment for demographics, CVD risk factors, and kidney function, the risks of all-cause death in the highest quartiles of serum phosphorus (>3.6 mg/dL), urine phosphorus-creatinine ratio (>0.55), and FE p; (>= 18%) were 1.63 (95% Cl, 1.23-2.17), 1.22 (95% Cl, 0.90-1.65), and 0.88 (95% Cl, 0.64-1.23), respectively, compared to the lowest quartiles of each. Results were similar for CVD death. Results also were similar in those with estimated glomerular filtration rate >= 60 and <60 m Umin/1.73 m(2). Limitations: Older all-male cohort. Few had advanced chronic kidney disease. Spot urine specimens were used. Conclusions: In community-living older men, higher serum phosphorus concentrations are associated with all-cause and CVD death. In contrast, urine phosphorus-creatinine ratio and FE,, are not. These findings do not support using urine phosphorus-creatinine ratio or FE,p; as adjuvant measures to predict risk of mortality or CVD in the general population. Am J Kidney Dis. 61(4):555-563. Published by Elsevier Inc. on behalf of the National Kidney Foundation, Inc. This is a US Government Work. There are no restrictions on its use.