Experiments have been designed to elucidate the varying degrees of destruction of intact hemoglobin (methemoglobin plus oxyhemoglobin) observed on application of the methemoglobin reduction test to normal and abnormal subjects. Surprisingly, the degree of intact hemoglobin destruction was found to vary directly with the rates of methemoglobin reduction, particularly via the pentose phosphate pathway in the presence of methylene blue, and inversely with cell age. In addition, confirmation was obtained of increased susceptibility to destruction of intact hemoglobin in subjects with such congenital or acquired defects of hemoglobin stability as might result from hemoglobin H, acute lead poisoning, or prior exposure to aromatic drugs.

Further evidence was presented that accumulation of methemoglobin militates against intact hemoglobin destruction. It was suggested that the methemoglobin content of samples of blood after application of the methemoglobin reduction test should be assessed in relation to the simultaneous changes in the intact hemoglobin concentrations of the incubation mixtures.

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