B2M and chronic kidney disease: Among the former, showing the most decreased levels in CKD, were fragments of collagen types I, II, III and XI, clusterin (CLU), uromodulin (UMOD) and mucin-12 (MUC12); whereas peptides originated from albumin, beta-2-microglobulin (B2M) and alpha-1-antitrypsin (A1AT) were the most increased.