Factors Which Interfere with the Benzidine and Meyer's Tests for Blood in Milk and Urine

Abstract

Summary

1. When milk and urine specimens containing, in some instances, even macroscopic amounts of red corpuscles, give false negative tests with the standard Meyer or benzidine reagents, the factors found at least partially responsible include: lessened fragility of the corpuscles; increased alkalinity of the specimen, producing alkaline hematin which does not respond: settling or entrainment of red corpuscles by the precipitating phosphates. 2. These factors may be controlled by pre-acidification and heating of the specimen, by storage for 12 to 24 hours at room temperature to increase hemolysis, or by centrifugation and making up to the original volume with distilled water to insure hemolysis. The latter treatment is recommended for urine samples which have been allowed to stand in the refrigerator.