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BACKGROUND:
In contemporary series, posterior urethral valves (PUV) leads to renal failure in up to one third of patients, with up to one quarter of patients eventually progressing to end stage renal failure (ESRF). Prognostic indicators in posterior urethral valves patients allow appropriate follow up planning and counselling of families of affected boys. Nadir creatinine (lowest creatinine during the first year following diagnosis) is a recognised indicator of future renal function. We recently described “creatinine velocity” (Cvel), the rate of change of creatinine following initial bladder drainage, as a new early predictor of renal outcome in neonatally diagnosed PUV.
We studied these two prognostic indicators in combination, as a test for future renal impairment in neonatally diagnosed PUV patients.
METHODS:
Medical records for patients treated by endoscopic valve ablation at our institution between 1993 and 2004 were reviewed. Data collected included timing of valve ablation, creatinine levels during the first year following diagnosis, and most recently documented renal function. Creatinine velocity and nadir creatinine were considered predictive of future renal failure if they were greater than 3umol/L/day or greater than 70umol/L respectively. Chronic renal insufficiency (CRI) was defined as CKD2 or higher according to Kidney Disease Outcomes Quality Initiative guidelines.
Outcomes in test groups were analysed by Fisher exact test. Statistical significance was defined as P < 0.05.
RESULTS:
A total of 129 patients were identified. Of these, progress notes were available for 120 patients. Bladder drainage was established within the neonatal period (first 30 days of life) in 65 patients. Both Cvel and nadir creatinine were available for 62 patients. Mean follow up was 9.4years.
Patients were grouped as having both risk factors (Group A), having one risk factor (Group B) or having neither risk factor (Group C). Renal impairment developed in 4 of 4 (100%) patients from Group A, compared with 11 of 18 (61.1%) patients from Group B and 3 of 40 (7.5%) patients from Group C (P=<0.0005). All 3 patients from group C with renal impairment had CKD2.
As a diagnostic test for future development of renal failure, “presence of at least one of these risk factors” had a specificity of 84.1%, sensitivity of 83.3%, positive predictive value of 68.2% and negative predictive value of 92.5%.
CONCLUSIONS:
Considered together, these prognostic indicators provide a powerful test for future development of CRI in neonatally diagnosed PUV patients. Patients who do not have either of these risk factors are highly unlikely to develop CRI.