Carbamylated hemoglobin (CarbHb) levels expressed as valipe hydantoin (VH) were measured by high performance liquid chromatography (HPLC) in patients with acute renal failure (ARF, n=35) and chronic renal failure (CRF, n=39). CarbHb levels in CRF patients were approximately 2.5 times of those in ARF ones (121.2 +/- 8 vs 54.8 +/- 6 microgVH/gHb, p<0.01). CarbHb levels of 80 microgVH/gHb provided the best statistical values (sensitivity of 89% and specificity of 82%). CarbHb/BUN and Carb/Cr ratios were also effective determinants in differentiation between ARF and CRF. CarbHb/BUN ratio of 1.5 and CarbHb/Cr ratio of 20 were the best statistical cut off points. As such, measurement of CarbHb levels could be a reliable non-invasive method in identifying ARF from CRF patients.