Hypothesis / aims of study
In order to maintain renal function, it is very important for patients with spina bifida (SB) to receive feasible urological management and avoid to febrile urinary tract infection (fUTI) during their lifetime. Therefore, it is very important to evaluate renal function for SB patients. A patient’s renal function is usually evaluated with serum creatinine (SCre), renal scintigram and ultrasonography comprehensively; however, SCre and the estimated glomerular filtration rate (eGFRcre), which is estimated by Scre, are strongly affected by the quantity of the patient’s muscle volume. It was previously reported that for patients with spinal cord injury, renal function evaluated by eGFRcre is likely to be overestimated, because of low muscle volume1). Nowadays, cystatin C (CysC), which is not influenced by muscle mass, has been introduced clinically to estimate renal function. It should be more accurate to evaluate renal function by eGFR that is estimated using CysC (eGFRcys) for SB patients who sometimes suffer impairment in their lower limbs in comparison to evaluation by eGFRcre. Therefore, the aim of this study is to investigate whether the estimation of renal function by eGFRcre is affected by the muscle mass of SB patients more than that evaluated by eGFRcys.
Study design, materials and methods
A total of 54 SB patients who had been admitted to our institute from 2018 to 2019 were retrospectively reviewed. Medical records of urological and orthopedic symptoms and treatment for urological diseases were investigated. Patients were divided into 2 groups; patients who were able to walk (WA) and those who required wheelchairs (WC). Discrepancies between values of estimated glomerular filtration rate with SCre and CysC were assessed in the ratio of eGRFcre and eGFRcys (eGFRcre/cys). The correlation between eGFRcre and eGFRcys was evaluated by the linear regression model. It was considered that the renal function was overestimated by eGFRcre when eGFRcre/cys was > 1.2. The value of eGFRcre and eGFRcys were calculated in formulas as follows; eGFRcre=194Cre-1.094Age-0.287(×0.739; in female) and eGFRcys={104CysC-1.019×0.996Age(×0.929; in female)}-8.
Interpretation of results
In this study, there was no visible correlation between eGFRcre and eGFRcys in the WC group and the value of eGFRcre was much higher than eGFRcys in all cases of WC, indicating that the patients’ renal function in the WC group was overestimated when the functions were evaluated by eGFRcre. Regarding eGFR in the WA group, the value of the correlation coefficient in the scatter plots was relatively low (r2=0.300), even though there was correlation between eGRFcre and eGFRcys. This is presumably because the renal function of some patients in the WA group who have a relatively lower muscle mass in their lower limbs were overestimated by eGFRcre. Patients using crutches could have potentially lower muscle mass in their lower limbs in comparison to those who walk on their own. However, there were not enough significant differences in the ratio of eGFRcre and eGFRcys between patients using crutches and those not using them in the WA group, because the number of patients using crutches was smaller (4 of 39 patients). These results indicated that renal function of SB patients with inability at the lower limbs could be overestimated when it is evaluated by eGRFcre.