Differentiation of acute from chronic renal impairment by detection of carbamylated haemoglobin.

Detection of carbamylated haemoglobin, measured as valine hydantoin per g haemoglobin (VH/g Hb), may be useful in differentiating between patients with acute or chronic renal failure. To assess this test, we measured carbamylated haemoglobin prospectively in 42 consecutive patients referred to the regional renal unit with a serum creatinine in excess of 500 mumol/L and a provisional diagnosis of acute renal failure (ARF). Patients were subsequently classed on clinical criteria as having ARF (20) or acute on chronic renal failure (AonCRF, 22). 24 patients with stable chronic renal failure (CRF), matched for degree of renal impairment, were also studied. Standard biochemical tests and haemoglobin were similar among the three groups. Patients with ARF of 10 or less days duration had a lower median (interquartile range [IQR]) carbamylated haemoglobin concentration than those with a longer duration of ARF (29 [27-35] vs 72 [60-83] micrograms VH/g Hb; p < 0.01). Carbamylated haemoglobin concentration was lower in the ARF group than in the AonCRF or CRF groups (42 [31-67], 116 [83-119], and 148 [122-210] micrograms VH/g Hb, respectively; p < 0.001). All patients with a degree of acute and potentially, reversible renal failure (ARF and AonCRF) had a carbamylated haemoglobin concentration below 190 micrograms VH/g Hb (sensitivity 100%, positive predictive value 62% for this cut-off). When the ratio of carbamylated haemoglobin to serum creatinine was calculated, to correct for degree of renal failure, a value of less than 0.2 had a 100% sensitivity and 80% positive predictive value for dividing patients with potentially reversible renal failure from those with CRF. Measurement of carbamylated haemoglobin was useful in identifying patients with acute and potentially reversible forms of renal failure. This test could be of clinical value in deciding which patients require urgent referral for further management and treatment in hospitals without specialist nephrological care.