A new study conducted by researchers from Aarhus University, Denmark, introduces a groundbreaking urine acid/base score. This innovative tool assesses tubular acid excretion capacity and identifies early acid retention, a condition linked to a higher risk of chronic kidney disease (CKD) progression.
Acidosis is a well-known factor that exacerbates kidney function decline in CKD. However, current assessments rely on plasma measures, which may miss subclinical acidosis, a covert condition occurring before plasma markers reflect acid retention. The urine acid/base score bridges this diagnostic gap, offering a reliable marker for early acid retention and risk assessment.
The study analyzed 24-hour urine samples from 213 patients with CKD stages 3 and 4, divided into three cohorts:
- Development cohort (N=82)
- Variation cohort (N=58)
- Validation cohort (N=73)
Subclinical acidosis was defined as an acid/base score below the 95% prediction interval of healthy controls. Outcomes included changes in measured GFR after 18 months and CKD progression over a median follow-up of six years (defined as a ≥50% decline in eGFR, initiation of long-term dialysis, or kidney transplantation).
Key Findings and Results
- Novel Biomarker: The urine acid/base score combines urinary pH and NH4+ excretion to evaluate both the demand and capacity for acid excretion, providing a comprehensive assessment of acid retention in CKD.
- Early Detection: Subclinical acidosis, undetectable by plasma measures, was prevalent in about 67% of participants across all cohorts.
- Risk Prediction:
- Patients with subclinical acidosis experienced an 18% larger decrease in measured GFR over 18 months.
- They faced an elevated risk of CKD progression, with adjusted hazard ratios of 9.88 in the development cohort and 11.1 in the validation cohort.
- Enhanced Predictive Value: The acid/base score demonstrated superior predictive accuracy for CKD progression compared to NH4+ excretion alone.
This study highlights the potential of the urine acid/base score as a critical tool for early detection and risk stratification in CKD. The findings emphasize the need for further research to:
- Investigate whether interventions can improve low acid/base scores.
- Determine if these improvements lead to meaningful clinical outcomes.
The introduction of this score marks a significant advancement in nephrology, paving the way for enhanced management and prognosis of CKD patients.