Carbamylated hemoglobin in hemodialysis patients

We have previously found that carbamylated hemoglobin (carHb) levels are increased in chronic renal failure and correlate positively with blood urea nitrogen (BUN) levels and with the duration of exposure to urea. In a fashion analogous to glycosylated hemoglobin in diabetic patients, it is possible that carHb may better reflect BUN levels before hemodialysis (preBUN) and also between hemodialysis sessions. We therefore tested the hypothesis that carHb could be a better index of adequacy of hemodialysis than the urea reduction ratio (URR). Fifty hemodialysis patients had carHb measured every 2 months for 14 months; the carHb level was compared with URR and preBUN levels, as assessed by changes in absolute numbers and trends of the BUN levels between hemodialyses. Mean URR was above 61% throughout the 14 months. Mean carHb levels did not change significantly during the study and were only weakly correlated with URR. However, there was a much better correlation between predialysis BUN and carHb, suggesting that carHb levels reflect more accurately the changes in BUN between hemodialysis sessions. To further test this hypothesis, we subdivided the patients arbitrarily, depending on the change in preBUN between two consecutive carHb measurements. We found significantly lower carHb levels when BUN decreased or remained stable than when it increased or was persistently high. In patients with decreasing or stable BUN, carHb was significantly lower than in patients with persistently high or increasing BUN (carHb 81.5 +/- 3.6 microg valine hydantoin [VH]/g Hb v 123.7 +/- 11.7 microg VH/g Hb, respectively; P < 0.001). URR was not different between groups. In addition to changes in BUN levels, carHb was correlated by multiple regression analysis with the presence of diabetes, weight, and plasma HCO3. The relationship between diabetic patients and carHb levels was complex because such patients tend to have higher preBUN levels, higher protein catabolic rate, and lower HCO3 levels. These results demonstrate that carHb reflects the changes between dialysis BUN and may serve as a more accurate index of uremia control. Clinically, it appears that well-dialyzed patients have carHb levels lower than 100 microg VH/g Hb.