Overestimation of glomerular filtration rate calculated from serum creatinine as compared with cystatin C in patients with subclinical hypercortisolism: Hyogo Adrenal Metabolic Registry.

The skeletal muscle mass are decreased in the patients with hypercortisolism. Glomerular filtration rate (eGFR) is not accurately evaluated by calculation from serum creatinine (eGFRcre) in these patients. However, it is not known whether it applies to patients with subclinical hypercortisolism. We investigated the dissociation between eGFRcre and eGFR calculated from cystatin C (eGFRcys) in patients with subclinical hypercortisolism and its association with the skeletal muscle mass. This cross-sectional study includes 23 patients with overt Cushing's syndrome (CS), 84 patients with possible autonomous cortisol secretion (pACS) and 232 patients with non-functioning adenomas (NFA). eGFRcre, eGFRcys, the ratio of eGFRcre to eGFRcys (eGFRcre/eGFRcys) were calculated. Skeletal muscle index (SMI) was measured by a direct segmental multi-frequency bioelectrical impedance body composition analyzer. eGFRcre/eGFRcys was significantly higher (p < 0.01) in pACS (mean +/- standard error: 1.15 +/- 0.02) than NFA (1.06 +/- 0.01). In multiple linear regression analysis, the presence of pACS (beta = 0.162, p < 0.01), and post 1 mg-DST cortisol levels (beta = 0.190, p < 0.01) were significantly associated with eGFRcre/eGFRcys independent of age, gender, BMI and diabetes. eGFRcre/eGFRcys was significantly and inversely associated with SMI (r = -0.164, p = 0.02). Furthermore, post 1 mg-DST cortisol levels was significantly associated with SMI in simple (r = -0.177, p = 0.01) and multiple (beta = -0.089, p = 0.01) regression analyses. In conclusion, dissociation between eGFRcre and eGFRcys was observed in patients with subclinical hypercortisolism at least partly explained by muscle mass. Our findings raise an important clinical point that eGFRcre value should be carefully evaluated even in the phase of subclinical hypercortisolism.