Method for measuring increased plasma hemoglobin in the presence of erythrocytes

Despite its many drawbacks the classic benzidine technique is the method most widely used for determining plasma hemoglobin. An additional disadvantage, reported here, is that the method measures hemoglobin in erythrocytes as well as in plasma. Thus, if plasma specimens are accidentally contaminated with erythrocytes, apparent free hemoglobin in plasma will be artifactually high. Although the present method lacks the sensitivity of the benzidine technique, it self-corrects for the presence of erythrocytes. We have found it particularly useful for specimens of rodent (rat mouse) blood, where some cells appear to resist centrifugation, where the small sample sizes frequently result in accidental contamination of plasma with cells, and where normal values may be higher than those for human plasma.