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Phosphate handling by end‐stage kidneys and benefits of residual renal function on phosphate removal in patients on haemodialysis
Author(s) -
Iwasawa Hideaki,
Nakao Toshiyuki,
Matsumoto Hiroshi,
Okada Tomonari,
Nagaoka Yume,
Wada Toshikazu
Publication year - 2013
Publication title -
nephrology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 61
eISSN - 1440-1797
pISSN - 1320-5358
DOI - 10.1111/nep.12039
Subject(s) - medicine , renal function , endocrinology , fibroblast growth factor 23 , phosphate , excretion , parathyroid hormone , creatinine , uremia , urinary system , population , urology , chemistry , calcium , biochemistry , environmental health
Aim We investigated the handling of phosphate by end‐stage kidneys and the contribution of residual renal function ( RRF ) to phosphate homeostasis in haemodialysis patients. Methods Blood and 24 h urinary specimens were obtained from 79 consecutive chronic haemodialysis patients with a urinary output greater than 100 mL/day. Thirty‐five patients with a glomerular filtration rate ( GFR ) ≥ 3.0 mL/min were included as group A, and 44 patients with GFR < 3.0 mL/min as group B . Additionally, the whole dialysed fluids during a session of haemodialysis were collected from another nine patients. Concentrations of phosphate, creatinine, urea nitrogen, intact parathyroid hormone (i PTH ) and fibroblast growth factor 23 ( FGF ‐23) were measured. Results Twenty‐four hour urinary phosphate excretion ( UPE ) was 283 ± 115 and 139 ± 57 mg/day (9.1 ± 3.5 and 4.5 ± 1.8 mmol/day) in groups A and B , respectively. Tubular reabsorption of phosphate ( TRP ) was 39.2 ± 13.3 and 31.7 ± 13.6% in groups A and B , respectively ( P = 0.02). UPE significantly correlated with GFR (r = 0.85, P < 0.001) and PTH (r = 0.44, P < 0.001), but not with FGF ‐23, in the entire patient population. The correlation between UPE and intact PTH levels was absent in group B . Weekly UPE in group A was significantly greater ( P < 0.001), while that in group B was similar to the amount of phosphate removed by a haemodialysis session. Conclusions Urinary phosphate excretion by end‐stage kidneys depends more on GFR than diminishing TRP . The action of PTH on the kidneys remains until GFR decreases to as low as 3 mL/min. Residual renal function plays a significant role in phosphate elimination, and it is possible that FGF ‐23 no longer acts effectively to excrete phosphate in the urine in these patients.