Cross-sectional analysis of abnormalities of mineral homeostasis, vitamin D and parathyroid hormone in a cohort of pre-dialysis patients. The chronic renal impairment in Birmingham (CRIB) study.
BACKGROUND
Disturbances in mineral and vitamin D metabolism, which affect parathyroid hormone (PTH) synthesis, are well recognized in patients receiving dialysis. However, it is unclear at what stage of chronic kidney disease (CKD) these abnormalities develop.


METHODS
The associations between CKD stages 3 and 5, and alterations of calcium, phosphate, vitamin D and PTH concentrations were assessed in 249 patients (mean age 61 years, 66% male) and 79 age- and sex-matched healthy controls.


RESULTS
As compared to controls, serum phosphate concentrations were elevated among CKD patients (1.40 vs. 1.11 mmol/l; p < 0.0001). And levels of both 25-hydroxyvitamin D (42.1 vs. 60.4 nmol/l; p < 0.0001) and 1,25-dihydroxyvitamin D (58.2 vs. 119.5 pmol/l; p < 0.0001) were lower among patients with CKD, even among those with only stage 3 CKD and despite 73% of patients receiving vitamin D supplements. The ratio of 1,25-dihydroxy- to 25-hydroxyvitamin D was lower than controls, even among patients with stage 3 CKD (p = 0.0001), and this ratio diminished with advancing renal impairment. Concomitant elevations were observed in intact PTH (13.8 vs. 4.2 pmol/l; p < 0.0001) and whole PTH (7.9 vs. 2.7 pmol/l; p < 0.0001).


CONCLUSIONS
Impaired conversion of 25-hydroxy- to 1,25-dihydroxyvitamin D is an early feature of renal disease, and progresses as renal function deteriorates.
Zehnder
Daniel
D
Department of Nephrology, University Hospital Coventry and Warwickshire NHS Trust, Coventry, UK. d.zehnder@warwick.ac.uk
Landray
Martin J
MJ
Wheeler
David C
DC
Fraser
William
W
Blackwell
Lisa
L
Nuttall
Sarah
S
Hughes
Sue V
SV
Townend
John
J
Ferro
Charles
C
Baigent
Colin
C
Hewison
Martin
M
D000368:Aged; D002118:Calcium / Q000097:blood*; D003430:Cross-Sectional Studies; D005260:Female; D006706:Homeostasis; D006801:Humans; D006961:Hyperparathyroidism / Q000097:blood* / Q000209:etiology; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000150:complications / Q000534:rehabilitation; D008297:Male; D008875:Middle Aged; D008903:Minerals / Q000097:blood; D010281:Parathyroid Hormone / Q000097:blood*; D010710:Phosphates / Q000097:blood*; D006435:Renal Dialysis / Q000009:adverse effects*; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood* / Q000209:etiology
D008903:Minerals; D010281:Parathyroid Hormone; D010710:Phosphates; D014807:Vitamin D; D002118:Calcium