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Kidney Week

Abstract: FR-PO1159

Serum Phosphate Levels Modify the Impact of Intact PTH Levels on Renal Outcomes in Kidney Transplant Recipients

Session Information

Category: Transplantation

  • 1902 Transplantation: Clinical

Authors

  • Doi, Yohei, Osaka University Graduate School of Medicine, Suita Osaka, Japan
  • Hamano, Takayuki, Osaka University Graduate School of Medicine, Suita Osaka, Japan
  • Yamaguchi, Satoshi, Osaka University Graduate School of Medicine, Suita Osaka, Japan
  • Oka, Tatsufumi, Osaka University Graduate School of Medicine, Suita Osaka, Japan
  • Sakaguchi, Yusuke, Osaka University Graduate School of Medicine, Suita Osaka, Japan
  • Matsui, Isao, Osaka University Graduate School of Medicine, Suita Osaka, Japan
  • Isaka, Yoshitaka, Osaka University Graduate School of Medicine, Suita Osaka, Japan
Background

Mineral bone disorder (MBD) parameters including parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), calcium, phosphate (P), 1,25-dihydroxyvitamin D (1,25D), and 25-hydroxyvitamin D predict renal outcomes, when assessed separately, in kidney transplant recipients (KTRs). However, data evaluating those parameters simultaneously and interwoven relationships on renal outcomes are scarce.

Methods

In this single-center prospective cohort study, we included 263 KTRs with grafts functioning at least 1 year after transplantation. The renal outcome was a composite of estimated GFR (eGFR) halving and graft loss. We performed Cox regression analyses to assess associations of MBD parameters with the renal outcome.

Results

Median eGFR was 38 ml/min/1.73m2.The renal outcome occurred in 98 KTRs during a median follow-up of 10.7 years. In a multivariable Cox model, intact PTH (iPTH), P, and 1,25D, but not intact FGF23 levels, were associated with the renal outcome (HR 1.60 per log scale; 95%CI 1.19-2.14, 1.60 per mg/dL; 1.14-2.23, 0.98 per pg/mL; 0.96-1.00, and 0.99 per log scale; 0.74-1.34, respectively). A competing risk analysis with death as a competing event yielded a similar result. After stratification into 4 groups by the median values of iPTH and P (Pinteraction<0.1), however, high iPTH levels (69 ≥ pg/mL) were not associated with worse renal outcomes when serum P levels were less than median (3.2 mg/dL) (Figure). Only in KTRs not receiving oral active vitamin D, 1,25D levels predicted the renal outcome (Pinteraction<0.1).

Conclusion

High iPTH, P, and low 1,25D levels predicted poor renal outcomes in KTRs. Given that PTH promotes phosphaturesis and enhances 1α-hydroxylase activity in proximal tubules (PT), low P and high 1,25D levels may reflect viable PT function.

Hazard ratios for renal outcomes stratified by the median values of serum iPTH and phosphate levels