Kidney Week

Abstract: TH-PO1111

Estimated Proximal Tubule Fluid Phosphate Concentration as an Early Marker of Phosphate Metabolism Abnormalities and a Predictor of Kidney-Related Outcomes in Patients with CKD

Session Information

• CKD: Therapies, Innovations, and Insights
  November 06, 2025 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: CKD (Non-Dialysis)

• 2302 CKD (Non-Dialysis): Clinical, Outcomes, and Trials

Authors

• Tato, Wasako, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Wasako Tato, MD

• Tamaki, Hiroyuki, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Hiroyuki Tamaki, MD

• Eriguchi, Masahiro, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Masahiro Eriguchi, MD, PhD

• Kosugi, Takaaki, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Takaaki Kosugi, MD, PhD

• Uemura, Takayuki, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Takayuki Uemura, MD

• Furuyama, Riri, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Riri Furuyama, MD

• Nishimoto, Masatoshi, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Masatoshi Nishimoto, MD

• Tanabe, Kaori, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Kaori Tanabe

• Okamoto, Keisuke, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Keisuke Okamoto, MD, PhD

• Matsui, Masaru, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Masaru Matsui, MD, PhD

• Samejima, Ken-ichi, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Ken-ichi Samejima, MD, PhD

• Tsuruya, Kazuhiko, Nara Kenritsu Ika Daigaku, Kashihara, Nara Prefecture, Japan

Kazuhiko Tsuruya, MD, PhD

Background

Although elevated estimated proximal tubule fluid phosphate concentration (ePTFp) has been linked to tubular damage in mouse models and human cross-sectional studies, prospective observational studies assessing the relationship between ePTFp and kidney-related outcomes in patients with chronic kidney disease (CKD) are lacking. This study evaluated the association between ePTFp and kidney-related outcomes, and the modifying effect of phosphate regulatory biomarkers in CKD patients.

Methods

Patients were recruited at Nara Medical University between 2020 and 2022 and prospectively followed until the end of March 2024. The association between baseline ePTFp (urine phosphate/creatinine concentration × serum creatinine level × 3.33) and the risk of a 40% decline in estimated glomerular filtration rate (eGFR) or progression to kidney failure requiring replacement therapy (KFRT) was examined using a Cox proportional hazards model.

Results

Among the 796 patients (median age, 71 years; 63.9% males; median eGFR, 38.5 mL/min/1.73 m²; and median ePTFp, 2.1 mg/dL), 199 reached the composite endpoint of a 40% decline in eGFR or initiation of KFRT during a median follow-up of 26.9 months. Restricted cubic spline analysis demonstrated that ePTFp exhibited an inflection point and subsequently increased beyond the upper limits of the serum levels of fibroblast growth factor 23 (25 pg/mL), intact parathyroid hormone (45.3 pg/mL), and phosphate (3.5 mg/dL). In contrast, ePTFp showed a consistent upward trend with decreasing levels of 1,25-dihydroxyvitamin D₃. No significant association was observed between ePTFp and daily urinary phosphate excretion. Log-transformed ePTFp was independently and incrementally associated with an increased risk of kidney-related outcome (hazard ratio [95% confidence interval]: 1.66 [1.06–2.61]). Additionally, no interaction effect was observed in the subgroup analysis stratified by CKD-mineral and bone disorder markers.

Conclusion

Compared with conventional markers, ePTFp is an early indicator of phosphate metabolism abnormalities and may serve as a reliable prognostic biomarker for adverse kidney outcomes in CKD patients.

Funding

• Private Foundation Support

Digital Object Identifier (DOI)

• doi: 10.1681/ASN.2025r9hk6ag0