Estimated Glomerular Filtration Rate Using Cystatin C is a More Sensitive Marker for Kidney Dysfunction in Nonweight-bearing Individuals.

PURPOSE

Individuals with neuromuscular disorders and neurogenic lower urinary tract dysfunction are commonly nonweight-bearing with lower lean muscle mass than the general population. We sought to compare estimated glomerular filtration rate equations that include creatinine, cystatin C, or both, in nonweight-bearing individuals and matched ambulatory controls.

MATERIALS AND METHODS

Records were reviewed for individuals with serum creatinine (Cr) and cystatin C (Cys) and diagnosis consistent with nonweight-bearing status, and matched ambulatory controls. The 2021 CKD-EPI (Chronic Kidney Disease-Epidemiology Collaboration) race agnostic equations were used to calculate estimated glomerular filtration rate. Renal function was compared by equation in the overall cohorts and in a patient subset with imaging and/or urinalysis evidence of renal dysfunction.

RESULTS

Nonweight-bearing (n = 102) and control populations (n = 204) had similar demographics. In the nonweight-bearing population, estimated glomerular filtration rate differed when calculated using CKD-EPI, CKD-EPI and CKD-EPI (107, 93, 80 mL/min/1.73 m, respectively, < .001). The differences in estimated glomerular filtration rate were greater in the nonweight-bearing relative to the control group regardless of CKD-EPI equation pairs compared ( < .001). In the patient subset with imaging and/or proteinuria evidence of renal dysfunction, the nonweight-bearing population again had different estimated glomerular filtration rate when calculated using CKD-EPI, CKD-EPI, and CKD-EPI (001). Fifty-eight percent of nonweight-bearing individuals with evidence of renal dysfunction on imaging or urinalysis were reclassified into a lower estimated glomerular filtration rate category when using estimated glomerular filtration rate relative to estimated glomerular filtration rate.

CONCLUSIONS

Estimated glomerular filtration rate equations containing serum creatinine, cystatin C, or both, validated in mostly ambulatory populations, are not equivalently accurate in estimating kidney function in nonweight-bearing individuals. Comparison of these equations against gold standard glomerular filtration rate measurement is needed to determine which most closely approximates true glomerular filtration rate.