Abstract
Fibroblast growth factor 21 (FGF21) is a member of the endocrine FGF family that acts as a metabolic regulator of both glucose and lipid metabolism. Similar to fibroblast growth factor 23 (FGF23), serum FGF21 levels rise progressively with the loss of renal function, reaching 20 times normal values in end-stage renal disease. In patients with chronic kidney disease (CKD), higher serum FGF21 levels correlate with poorer metabolic profile, higher inflammatory markers, more comorbidities, and higher mortality. The high serum FGF21 levels are above and beyond what can be explained by the loss of FGF21 renal clearance, suggesting increased production and/or impaired non-renal clearance. In diabetic nephropathy, serum FGF21 levels correlate with the severity of albuminuria and faster loss of glomerular filtrate rate and can potentially be a biomarker of poor prognostic. The observational and associative human data contrast sharply with in vitro and in vivo preclinical experimental data, which is more in line with a protective role of FGF21 in chronic nephropathies. We here review the physiology of FGF21, and the literature regarding its behavior in CKD with particular focus on diabetic nephropathy. Finally, we speculate on the role of FGF21 in CKD.