Analysis of hypophosphatemia in calcium nephrolithiasis.
OBJECTIVE
To analyze the pathophysiology of hypophosphatemia in calcium nephrolithiasis, we investigated the relation between serum phosphorus, 1,25-dihydroxyvitamin D, and parathyroid hormone (PTH) levels in 63 consecutive patients with calcium nephrolithiasis, comparing them with 26 age-matched control subjects.


RESULTS
Serum phosphorus concentrations in normocalciuric and absorptive hypercalciuric stone formers were significantly decreased compared with control subjects (P<0.001 and P<0.01, respectively). The fractional excretion (TRP) and renal threshold (TmP/GFR) of phosphorus were significantly decreased in the subjects with nephrolithiasis (P<0.01 and P<0.001, respectively). Serum phosphorus concentrations were inversely correlated with serum 1, 25-dihydroxyvitamin D in control subjects and in absorptive hypercalciuric stone formers (P<0.01 and P <0.05, respectively), suggesting that the physiologic relation between phosphorus and 1, 25-dihydroxyvitamin D is maintained in these patients. Serum phosphorus concentrations in absorptive hypercalciuric patients, although related to 1,25-dihydroxyvitamin D, were not related to PTH even though PTH and 1,25-dihydroxyvitamin D concentrations were directly related (P<0.05). The lack of a relation between PTH and serum phosphorus concentrations in absorptive hypercalciuric stone formers was similar to that in controls. In normocalciuric stone formers, there was no relation between serum 1,25-dihydroxyvitamin D and serum phosphorus, but PTH and 1,25-dihydroxyvitamin D were inversely correlated (P<0.05).


CONCLUSIONS
Abnormal renal tubular function with a depressed rate of renal phosphorus transport and an abnormal 1,25-dihydroxyvitamin D concentration is common in nephrolithiasis. Differences in the relations between phosphorus and 1,25-dihydroxyvitamin D observed in hypercalciuric v normocalciuric subjects suggest that the pathogenesis of proximal tubulopathy differs among patients with nephrolithiasis.
Yamakawa
K
K
Department of Urology, Mie University School of Medicine, Mie, Japan.
Kawamura
J
J
D000328:Adult; D000368:Aged; D002118:Calcium / Q000652:urine; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D017674:Hypophosphatemia / Q000097:blood* / Q000503:physiopathology*; D007669:Kidney Calculi / Q000097:blood* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010281:Parathyroid Hormone / Q000097:blood; D010758:Phosphorus / Q000097:blood; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
D010281:Parathyroid Hormone; D014807:Vitamin D; D010758:Phosphorus; C097949:1,25-dihydroxyvitamin D; D002118:Calcium