FGF21 and chronic kidney disease: In the present study, we investigated (1) the clinical correlation of circulating FGF21 in conjunction with physiological and pathological aspects in CKD patients, (2) the relationship between the change of circulation FGF21 levels and the development of CKD from early- to end-stage of disease, and (3) the effect of comorbidities of CKD to plasma FGF21 concentration.