BACKGROUND: The accuracy of creatinine-based estimated glomerular function (Schwartz eGFR) calculation has been questioned for patients with genitourinary abnormalities. Specifically, prior investigations have demonstrated potential important differences in Schwartz-eGFR and cystatin-c based eGFR (CysC-eGFR) in the neurogenic bladder (NGB) patients. Herein, we aim to understand the utility of CysC-eGFR in NGB and posterior urethral valve (PUV) patients.
METHODS: A prospectively maintained database of NGB and PUV patients with both serum creatinine and cystatin-C evaluations who were seen from February 2023 was used for evaluation. Patients were grouped based on diagnosis (NGB vs. PUV) and factors that correlated with differences in Schwartz-eGFR and CysC-eGFR were evaluated in each population. Clinical variables evaluated included age, sex, height, weight, BMI, and creatinine.
RESULTS: A total of 72 patients (36 NGB, 36 PUV) were identified (Table 1). Among NGB patients, 22.2% (8/36) had worse CKD stage based on CysC-eGFR compared to Schwartz-eGFR (median ∆eGFR -43.7, IQR -79.9 to -20.3; ;6 CKD stage 1 to stage 2; 2 CKD stage 2 to stage 3). Among PUV patients, 30.5% (11/36) had worse CysC-based eGFR (median ∆eGFR -26.7, IQR -52.5 to -13.5; 10 CKD stage 1 to stage 2; 1 CKD stage 1 to stage 3). For both NGB and PUV patients, there was a significant correlation with age and difference in two eGFRs (NGB: R=0.463, p=0.004; PUV: R=0.379, p=0.022, Figure 1). For NGB patients, there was a significant correlation with BMI and eGFR difference (R= 0.331, p=0.049; Figure 2).
CONCLUSIONS:
While limited by small numbers, Schwartz-eGFR, compared to CysC-eGFR, appears to overestimate eGFR for NGB and PUV patients who are younger. For NGB patients with high BMI, Schwartz-eGFR appears to underestimate eGFR. The clinical impact of this requires further evaluation due to small numbers and limited number of patients with higher CKD stages. Clinicians should be wary of interpreting serum creatinine based eGFR measurements for patients with genitourinary abnormalities and should consider CysC-based measurements in younger cohorts with abnormal BMIs.