Carboxyhemoglobin in the rat: Improvements in the spectrophotometric measurement and comparison to other studies

Abstract

An improved and simplified spectrophotometric method for the determination of carboxyhemoglobin (COHb) is described, which employs an equation to correct for the dissociation error during analysis. Two microliters, or less, of blood is diluted with an ammonium hydroxide solution directly in the measuring cuvette. A layer of light mineral oil overlying the diluent was found to increase measured COHb saturation of blood equilibrated with 100% CO. Sodium dithionite treatment of the oil further increased this value in one case. The measured COHb was shown to be affected directly by factors that alter hemoglobin concentration in the diluent (i.e. blood volume, hematocrit). Blood samples kept cold and under oil may be stored safely for as long as 10 days. Measurement of COHb by this method in rats exposed to 525, 900, 1800 and 2400 ppm CO produces higher values than those obtained with the 1965 spectrophotometric method of Commins and Lawther. Variations on the method of Commins and Lawther, as well as COHb values available in the literature for animals exposed to CO, are reviewed briefly.