Kidney Week

Abstract: FR-PO0516

Kidney Tubular Function and Adverse Outcomes in CKD

Session Information

• CKM: Clinical - Trials, Epidemiology, and Biomarkers
  October 23, 2026 | Location: Exhibit Hall A, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Cardiovascular-Kidney-Metabolic Health

• 602 Cardiovascular-Kidney-Metabolic Health: Clinical

Authors

• Andersen, Jesper Frank, Aarhus Universitet Faculty of Health, Aarhus, Central Denmark Region , Denmark

Jesper Frank Andersen, MD

• Leipziger, Jens G., Aarhus Universitet Faculty of Health, Aarhus, Central Denmark Region , Denmark

Jens G. Leipziger, MD, DrMed

• Buus, Niels Henrik, Aarhus Universitetshospital Afdeling Nyresygdomme, Aarhus, Central Denmark Region , Denmark

Niels Henrik Buus

• Nielsen, Sebastian, Aarhus Universitetshospital Afdeling Nyresygdomme, Aarhus, Central Denmark Region , Denmark

Sebastian Nielsen, MD

• Nyvad, Jakob, Aarhus Universitetshospital Afdeling Nyresygdomme, Aarhus, Central Denmark Region , Denmark

Jakob Nyvad, MD, PhD

• Birn, Henrik, Aarhus Universitetshospital Afdeling Nyresygdomme, Aarhus, Central Denmark Region , Denmark

Henrik Birn, MD, DrMed, PhD

• Sorensen, Mads Vaarby, Aarhus Universitet Faculty of Health, Aarhus, Central Denmark Region , Denmark

Mads Vaarby Sorensen, PhD

• Berg, Peder, Aarhus Universitet Faculty of Health, Aarhus, Central Denmark Region , Denmark

Peder Berg, MD, PhD

Background

Kidney function is typically assessed using eGFR and uACR, which primarily reflects glomerular function. However, most kidney tissue is comprised of the tubulointerstitial compartment. We recently developed the urine ammonium-pH index (uAPI) as a measure of kidney tubular function. Here, we assessed the prognostic relevance of a low uAPI, as a measure of impaired tubular function, and if its integration could affect clinical management.

Methods

Six independent cohorts of patients with CKD (n=818) were followed for up to 5 years (median: 4.9 years, IQR: 3.5-5). The primary outcome was CKD progression (≥50% eGFR reduction, eGFR<15, or kidney replacement therapy). Secondary outcomes were acute kidney injury, metabolic acidosis, hyperkalemia, acute hospitalizations, cardiovascular outcomes, and all-cause mortality. Associations between a low uAPI and outcomes were assessed in an individual patient data meta-analysis approach using cox proportional hazards models/negative binomal regression analyses and adjusted for demographics and risk factors (including eGFR and uACR). Using our initial two cohorts as development cohort (n=150) and the remaining cohorts as validation cohort (n=668), we assessed the potential clinical relevance of integrating the uAPI in risk stratification.

Results

A low uAPI was associated with an adjusted 7.3-fold higher risk of CKD progression (95% CI: 3.3-16) and a significantly increased risk for all secondary outcomes. Adding the uAPI to the KDIGO heatmap or the kidney failure risk equation improved classification (60-70%) and discrimination (3-4%) and decreased the proportion of patients classified as needing nephrology referral in both the development (~54% to ~46%) and validation cohort (~64% to ~54%) without missing any kidney events.

Conclusion

Poor tubular function, as indicated by low a uAPI, is independently associated with adverse outcomes in CKD. Inclusion of the uAPI into standard risk stratification approaches may potentially optimize referral patterns, decrease patient burden, and optimize health care resource utilization.

Funding

• Private Foundation Support