Relationship of phosphorus and calcium-phosphorus product with mortality in CKD.
BACKGROUND
Abnormalities of mineral metabolism are prevalent in patients with kidney failure and are associated with increased risk for cardiovascular events. There are limited data investigating relationships of phosphorus and calcium-phosphorus product with outcomes in patients with chronic kidney disease (CKD) stages 3 to 4.


METHODS
Serum phosphorus and calcium were measured at baseline in 840 participants from the randomized cohort of the Modification of Diet in Renal Disease Study. Survival status until December 31, 2000, was obtained from the National Death Index. Cox models were performed to assess the relationship of serum phosphorus level and calcium-phosphorus product with all-cause and cardiovascular disease (CVD) mortality.


RESULTS
Mean serum phosphorus level was 3.8 +/- 0.7 mg/dL (1.23 +/- 0.23 mmol/L), calcium-phosphorus product was 34.7 +/- 6.3 mg2/dL2, and glomerular filtration rate (GFR) was 33 +/- 12 mL/min/1.73 m2 (0.55 +/- 0.20 mL/s/1.73 m2). All-cause and CVD mortality rates were 25% and 15%. Serum phosphorus level was not related to all-cause mortality in multivariable models (P = 0.46). In unadjusted analysis, serum phosphorus level was associated with (hazard ratio [HR] per 1 mg/dL increase, 1.34; 95% confidence interval [CI], 1.05 to 1.71; P = 0.02) increased risk for CVD mortality, but this association was partly attenuated and not statistically significant after adjustment for GFR and other confounders (HR, 1.27; 95% CI, 0.94 to 1.73; P = 0.12). Calcium-phosphorus product was not associated with all-cause mortality in unadjusted (P = 0.23) or multivariate analysis (P = 0.35). Calcium-phosphorus product was related to CVD mortality in unadjusted (HR per 10 mg2/dL2 increase, 1.30; 95% CI, 1.01 to 1.69; P = 0.04) analysis, but this association was not statistically significant after adjustment for GFR and other confounders (HR, 1.22; 95% CI, 0.89 to 1.66; P = 0.23).


CONCLUSIONS
In the Modification of Diet in Renal Disease Study cohort, serum phosphorus level and calcium-phosphorus product were not statistically associated with all-cause or CVD mortality after adjustment for GFR; however larger studies with additional statistical power are needed to evaluate these relationships, especially in the context of current practice patterns in patients with CKD.
Menon
Vandana
V
Division of Nephrology, Department of Medicine, Tufts-New England Medical Center, Boston, MA, USA.
Greene
Tom
T
Pereira
Arema A
AA
Wang
Xuelei
X
Beck
Gerald J
GJ
Kusek
John W
JW
Collins
Alan J
AJ
Levey
Andrew S
AS
Sarnak
Mark J
MJ
D000328:Adult; D000368:Aged; D002097:C-Reactive Protein / Q000032:analysis; D002118:Calcium / Q000097:blood*; D002318:Cardiovascular Diseases / Q000401:mortality; D002423:Cause of Death; D002908:Chronic Disease; D015331:Cohort Studies; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000097:blood* / Q000401:mortality; D008297:Male; D008875:Middle Aged; D009026:Mortality; D010758:Phosphorus / Q000097:blood*; D016016:Proportional Hazards Models; D016032:Randomized Controlled Trials as Topic; D012306:Risk
D010758:Phosphorus; D002097:C-Reactive Protein; D002118:Calcium