Determinants of haemoglobin carbamylation in haemodialysis and peritoneal dialysis patients.

BACKGROUND: Carbamylation is an irreversible process of non-enzymatic modification of proteins by the breakdown products of urea. For haemoglobin (Hb), the extent of carbamylation is a marker of urea exposure and has been proposed as an indicator of the control of uraemia by dialysis, analogous to the use of Hb glycosylation in diabetic patients. METHODS: We performed a cross-sectional study of haemodialysis (HD) and peritoneal dialysis (PD) patients in order to study potential determinants of carbamylated Hb (CarbHb) and to investigate the relationship between CarbHb and established measures of dialysis dose/adequacy by multivariate analysis. RESULTS: In 80 HD patients, CarbHb was independently predicted by post-dialysis urea (r=0.40, P:<0.01), serum albumin (r=0.24, P:<0.05) and serum bicarbonate (r=-0.40, P:<0. 05). No correlation was found between CarbHb and measures of dialysis dose/adequacy (Kt/V, urea reduction ratio, weekly dialysis duration, and normalized protein catabolic rate (nPCR)). In 42 PD patients, serum urea was the only significant independent predictor of CarbHb (r=-0.51, P:=0.001). No relationship was found between CarbHb and Kt/V, corrected creatinine clearance (CrCl) or nPCR in PD patients. CONCLUSIONS: Serum urea is the most consistent independent predictor of CarbHb in dialysis patients. This association in combination with the lack of a relationship with conventional measures of dialysis dose and a positive relationship with serum albumin suggest that a single measurement of CarbHb is unlikely to be a useful indicator of the adequacy of dialysis.