CST3 and obesity due to melanocortin 4 receptor deficiency: Use of cystatin C as a filtration marker of kidney function has been criticized owing to the presence of non-GFR determinants including inflammation, obesity, diabetes, smoking, and thyroid disease.35,36,37,38 The use of eGFRcys may have a greater association with long-term outcomes because it is capturing aspects of cardiometabolic risk that are unrelated to kidney function.