Dialysis vintage and parathyroid hormone level, not fibroblast growth factor-23, determines chronic-phase phosphate wasting after renal transplantation.
OBJECTIVE
Fibroblast growth factor 23 (FGF23), rather than parathyroid hormone (PTH), has been shown to be the major factor behind hypophosphatemia in the early period after renal transplantation. However, it is not clear whether phosphate wasting persists in the chronic phase. Purpose of our study is to elucidate whether FGF23 can also explain phosphate wasting, if any, in the chronic phase.


METHODS
In this cross-sectional observational study, we enrolled 247 recipients who had received a graft more than 1 year prior to this study. We compared the phosphate metabolism of recipients and predialysis chronic kidney disease (CKD) patients who are matched on age and estimated glomerular filtration rate (eGFR). We also investigated the determinants of tubular reabsorption of phosphate normalized for glomerular filtration rate (TmP/GFR), as an index of renal threshold for phosphate.


RESULTS
Recipients had a median dialysis vintage of 27.0 months and eGFR 41.2 mL/min/1.73 m(2). Whereas hypophosphatemia (<2.4 mg/dL) was observed in 6.1% of the recipients, 55.2% had TmP/GFR lower than 2.4 mg/dL. Recipients showed significantly lower TmP/GFR in all CKD stages than their predialysis counterparts, indicating that phosphate wasting persists in the chronic phase. Compared to predialysis patients, the recipients in stages 2T and 3T showed lower phosphate and higher intact PTH levels, despite a higher percentage being active vitamin D users. However, in stage 4T, phosphate retention masked relative hypophosphatemia. FGF23 was higher in the recipients across all CKD stages, but adjustment for vitamin D prescription revealed that transplantation had no effect on FGF23. Multiple regression analysis in the recipients showed significant negative associations of intact PTH and dialysis vintage with TmP/GFR.


CONCLUSIONS
Renal phosphate wasting persists in the chronic-phase renal transplantation recipients even with normophosphatemia. Persistent hyperparathyroidism and longer dialysis vintage, not FGF23, was associated with renal phosphate wasting in the chronic phase. Such an impact on phosphate metabolism of the factors determined in dialysis period could be called as "uremic memory". This novel finding in the chronic phase is in sharp contrast to the previous finding in the early phase that FGF23 levels are determinants of phosphate wasting.
Department of Kidney Disease and Hypertension, Osaka General Medical Center, 3-1-56 Bandai-higashi, Osaka, 558-8558, Japan.
Kodo
K
Tomida
Takayuki
T
Hamano
Naotsugu
N
Ichimaru
Naohiko
N
Fujii
Isao
I
Matsui
Norio
N
Nonomura
Yoshiharu
Y
Tsubakihara
Hiromi
H
Rakugi
Shiro
S
Takahara
Yoshitaka
Y
Isaka
D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D005919:Glomerular Filtration Rate; D006801:Humans; D017674:Hypophosphatemia / Q000097:blood* / Q000503:physiopathology; D007676:Kidney Failure, Chronic / Q000097:blood / Q000503:physiopathology / Q000601:surgery; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D006435:Renal Dialysis
C000717427:FGF23 protein, human; D010281:Parathyroid Hormone; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23