Kinetics of carbamylated haemoglobin in acute renal failure

Background. Carbamylation of proteins by isocyanic acid, the reactive form of cyanate derived from urea, is increased in uraemia and may contribute to uraemic toxicity. Kinetics of carbamylation that may reflect uraemic toxic ity is not clearly defined in acute renal failure (ARF). Methods. Twenty-eight patients with ARF and 13 with chronic renal failure ( CRF) were included in the study in order to determine changes in carbamylat ed haemoglobin concentration (CarHb) in ARF. The usefulness of this paramet er for differentiating ARF from CRF was also investigated. CarHb was measur ed by high-performance liquid chromatography after acid hydrolysis. Results. Mean CarHb level (expressed as mu g carbamyl valine per gram (CV/g ) Hb) was significantly higher in ARF (54.3+/-5.2) than in normal subjects (31.6+/-1.3). On admission, CarHb level was correlated with duration of ARF prior to hospitalization in the intensive care unit (r(2)=0.723, P<0.001). CarHb was significantly higher at recovery in the subgroup of patients req uiring haemodialysis than in the subgroup not requiring haemodialysis (82.4 +/-11.3 vs 46.7+/-5.2, P<0.01). Similarly dialysis patients lost more weigh t (8.6+/-1.4 vs 2.7+/-0.5 kg, P<0.005) and had higher averaged blood urea l evels in the 20 days prior to recovery (17.6+/-1.9 vs 11.3+/-1.8 mol/l, P<0 .05). After recovery, CarHb level decreased at a rate of 0.219 mu g CV/g Hb per day in patients with reversible renal insufficiency. CarHb concentrati on was higher in patients with CRF. A cut-off CarHb value of 100 mu g CV/g Hb had a sensitivity of 94% and a positive predictive Value of 94% for diff erentiating ARF from CRF. Conclusions. Kinetics of CarHb showed a near normal red blood cell life spa n in ARF. Changes in CarHb enabled, with a good sensitivity, the distinctio n to be made between patients who recovered from ARF and those with sustain ed renal impairment, whether due to prior CRF or resulting from parenchymal sequelae. Measurement of CarHb is valuable at clinical presentation of ARF in patients with an unknown medical history of renal disease.