Estimation of plasma and urinary hemoglobin by a rate spectrophotometric method

A method is described for estimating plasma and urinary hemoglobin concentrations as low as 3 mg/L. The assay measures at 528 nm the rate of peroxidation of chlorpromazine by hemoglobin and is not affected by ascorbate and bilirubin concentrations up to 500 mumol/L. Results by this method (mean +/- SD: 54.4 +/- 41.6 mg/L; n = 19) correlated well with those by a scanning spectrophotometric method (52.5 +/- 41.6 mg/L; r = 0.96) and a Coulter Instrument method (r = 0.99; Coulter method: 125 +/- 15 g/L; rate method: 122 +/- 15 g/L; n = 10, r = 0.99). The correlation for assays of 20 plasma samples by our method and a tetramethylbenzidine method was also good (r = 0.95) though the latter gave lower results (31.1 +/- 31.6 mg/L) than the chlorpromazine method (50.9 +/- 41.1 mg/L). The chlorpromazine rate method gave an intra- and interday CV of 7.9% and 9.7%, respectively, at a hemoglobin concentration of 31 mg/L.