G.P.173: Are current formulas for estimated glomerular filtration rate reliable in children and adolescents with Duchenne muscular dystrophy?

Abstract

Improved life expectancy and the need to monitor renal safety of new therapies have fueled interest in renal function in patients with Duchenne muscular dystrophy (DMD). We assessed the usefulness of estimated glomerular filtration rate (eGFR) formulas based on serum creatinine (sCr) and/or cystatin C (CysC) in children and adolescents with DMD. DMD patients have low sCr values since they have less muscle mass. SCr-based formulas may therefore have limitations. CysC, being independent of muscle mass, may serve as a valuable alternative for eGFR in DMD. In a prospective cross-sectional study, 18 patients (5–22 years) underwent 51 Cr-EDTA for GFR measurement (mGFR), blood and urine analysis. Values for renal clearance obtained with sCr-based, CysC-based and sCr/CysC-based eGFR formulas were compared to mGFR. Median mGFR was 128 ml/min/1.73 m 2 . Nine patients had a mGFR >P90 (135 ml/min/m 2 ). Because of very low sCr values (mean ± SD: 0.16 ± 0.07 mg/dL), sCr-based and sCr/CysC-based formulas overestimate GFR. Mean eGFR ± SD was 464.0 ± 264.1 ml/min/1.73 m 2 for Schwartz, 464.2 ± 269.4 ml/min/1.73 m 2 for Flanders Metadata, 178.7 ± 61.1 ml/min/1.73 m 2 for height-independent and 479.9 ± 327.0 ml/min/1.73 m 2 for the Q (height) equation. CysC values (0.78 ± 0.13 mg/L) are within normal adult reference ranges. However, sCr/CysC-based formulas result in mean eGFR ± SD of 154.2 ± 34.7 ml/min/1.73 m 2 for Zappitelli and 169.2 ± 43.7 ml/min/1.73 m 2 for Bouvet. Concerning CysC-based equations the mean eGFR ± SD was 153.8 ± 60.3 ml/min/1.73 m 2 for Larsson, 125.4 ± 21.9 ml/min/1.73 m 2 for Filler and 105.4 ± 19.1 ml/min/1.73 m 2 for Zappitelli. This study demonstrates that sCr-based and sCr/CysC-based formulas should not be used for eGFR in DMD. However, even though mGFR and CysC-based equations showed a better agreement, more research is needed to confirm the preliminary findings that CysC-based equations are suitable for eGFR in DMD patients.