High plasma phosphate as a risk factor for decline in renal function and mortality in pre-dialysis patients.
BACKGROUND
Hyperphosphataemia is associated with increased mortality in patients with chronic kidney disease (CKD) stage IV or on dialysis. Furthermore, in animal studies, elevated plasma phosphate has been shown to be associated with an accelerated decline in renal function. The aim of this study was to determine the association of plasma phosphate with renal function loss and mortality in CKD stage IV-V pre-dialysis patients with GFR <20 ml/min/1.73 m(2).


METHODS
Incident pre-dialysis patients were included between 1999 and 2001 in the multi-centre PREPARE study, and followed until 2003 or death. Rate of decline in renal function for each patient was calculated by linear regression using the Modification of Diet in Renal Disease (MDRD) formula to estimate GFR (eGFR).


RESULTS
A total of 448 patients were included [mean (SD) age 60 (15) years, eGFR 13 (5.4) ml/min/1.73 m(2), decline in renal function 0.38 (0.95) ml/min/month]. Phosphate concentration at baseline was 4.71 (1.16) mg/dl, calcium 9.25 (0.77) mg/dl and calcium-phosphate product 43.5 (10.9) mg(2)/dl(2). For each mg/dl higher phosphate concentration, the mean (95% CI) decline in renal function increased with 0.154 (0.071-0.237) ml/min/month. After adjustment, this association remained [beta 0.178 (0.082-0.275)]. Seven percent of the patients died. Crude mortality risk was 1.25 (0.85-1.84) per mg/dl increase in phosphate, which increased to 1.62 (1.02-2.59) after adjustment.


CONCLUSIONS
High plasma phosphate is an independent risk factor for a more rapid decline in renal function and a higher mortality during the pre-dialysis phase. Plasma phosphate within the normal range is likely of vital importance in pre-dialysis patients.
Voormolen
Nora
N
Department of Clinical Radiology, Leiden University Medical Center, Albinusdreef 2, 2300 RC Leiden, The Netherlands. e.m.c.voormolen@lumc.nl
Noordzij
Marlies
M
Grootendorst
Diana C
DC
Beetz
Ivo
I
Sijpkens
Yvo W
YW
van Manen
Jeannette G
JG
Boeschoten
Elisabeth W
EW
Huisman
Roel M
RM
Krediet
Raymond T
RT
Dekker
Friedo W
FW
D000368:Aged; D000465:Algorithms; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D054559:Hyperphosphatemia / Q000150:complications* / Q000175:diagnosis; D007668:Kidney / Q000378:metabolism* / Q000473:pathology*; D007676:Kidney Failure, Chronic / Q000150:complications / Q000378:metabolism* / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D010710:Phosphates / Q000097:blood*; D012044:Regression Analysis; D006435:Renal Dialysis / Q000379:methods*; D012307:Risk Factors; D016896:Treatment Outcome
D010710:Phosphates