Combined creatinine velocity and nadir creatinine: A reliable predictor of renal outcome in neonatally diagnosed posterior urethral valves

Abstract

Nadir creatinine (lowest creatinine during the first year following diagnosis) is a recognised indicator of future chronic renal impairment (CRI) in posterior urethral valve (PUV) patients. We recently described "creatinine velocity" (Cvel), the rate of change of creatinine following initial bladder drainage, as a new early predictor of CRI in neonatally diagnosed PUV. Rising Cvel (>3 μmol/L/day) is associated with increased risk of CRI. We studied these two prognostic indicators in combination, as a test for future CRI in neonatally diagnosed PUV patients. Medical records for patients treated by endoscopic valve ablation at our institution between 1993 and 2004 were reviewed. Simple linear regression was used to calculate Cvel. Creatinine velocity and nadir creatinine were considered predictive of future CRI if they were greater than 3 μmol/L/day or greater than 75 μmol/L (0.85 mg/dL), respectively. Chronic renal insufficiency was defined as CKD2 or higher. Outcomes in test groups were analysed by Fisher exact test. Statistical significance was defined as p < 0.05. Sixty-two patients were treated within the first 30 days of life and had sufficient data to calculate both Cvel and nadir creatinine. Mean follow-up was 9.4 years. Patients were grouped as having both risk factors (Group A), one risk factor (Group B), or neither risk factor (Group C). All four (100%) patients from Group A developed CRI, compared with 11 of 17 (64.7%) patients from Group B and three of 41 (7.3%) patients from Group C (p ≤ 0.0005). As a diagnostic test for future CRI, "presence of at least one risk factor" had a specificity of 86.4%, sensitivity of 83.3%, positive predictive value of 71.4%, and negative predictive value of 92.7%. Additional prognostic information was obtained by assigning a score from 1 to 3 for each prognostic indicator (Table). The sum of these scores gave a PUV Risk Score. No patient with a PUV Risk Score of 2 developed CRI, while all patients with a Score of 6 developed CRI. Incidence of CRI in patients with PUV Risk Scores of 3, 4, and 5 was 8.3%, 50%, and 63.6%, respectively (p ≤ 0.0005). Considered together, these prognostic indicators provide a powerful test for future CRI. Presence of at least one of these risk factors should be considered "at risk for CRI". Patients with neither risk factor are unlikely to develop CRI. Calculation of the PUV Risk Score provides an even more accurate prognosis.