USP18 and chronic kidney disease: The goal of our study was to assess the association between serum and urine USP18 concentrations, cardiovascular risk factors, and different biomarkers of kidney disease in patients at different stages of chronic kidney disease (CKD), i.e., those with a biopsy-based diagnosis of glomerular pathology with proteinuria, those with CKD with an estimated glomerular filtration rate (eGFR) lower than 60 mL/min/1.73 m2, patients after kidney transplantation, and those treated with hemodialysis because of end-stage renal disease (ESRD).