Introduction: Estimated Glomerular Filtration Rate (eGFR) is the standard method for determining kidney function and chronic kidney disease (CKD) stage classification. In the Spina Bifida (SB) population, eGFR estimates from a creatinine-based equation may not accurately represent kidney function due to the lower muscle mass in this population. We hypothesized that estimating equations utilizing Cystatin-C (CysC) would yield different CKD classifications than Creatinine (Cr) – based equations for the adult SB population.
Methods: We conducted a retrospective chart review of all patients seen in an adult urology clinic with a diagnosis of spina bifida from 2004-2021 that were managed in our urology clinic with creatinine and cystatin C values available. All patients were > 18 years old. A cross-sectional study of patients with a CysC and concurrent Cr measurement was performed; the most recent lab values were utilized if multiple existed. Three adult eGFR equations were utilized. Patients were staged based on CKD classification (GFR > 90, GFR 60-90, GFR <60). A Chi-square test was conducted to determine the difference in CKD classification based on each equation.
Results: A total of 105 SB patients (63% female) were included in cross-sectional analysis. The mean age was 33 ± 6.5 years. Medical comorbidities including diabetes (12.4%), hypertension (28.6%), obesity (34.2%) were noted. Table 1 shows the difference in eGFR and CKD classifications between equations. On Chi-square analysis, CKD classifications were significantly different by the type of equation used (p = 0.007). Pair-wise comparison showed that significance was driven by the difference between cystatin C and creatinine equations (p = 0.002) and the cystatin C and combined equations (p = 0.05).
Conclusions: In an adult SB population, CysC-based equations result in lower eGFRs and different CKD classifications. Determining an appropriate eGFR measurement is essential to assessing and managing renal function in these medically complex patients.
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