Circulating FGF21 level was independently associated with CIN (aOR: 4.66, 95% CI: 1.29–16.86, p = 0.019) and renal function decline (aHR: 7.98, 95% CI: 4.07–15.66, p < 0.001) whether diabetes was present or not. This evidence concerns the gene FGF21 and diabetes mellitus.