Standardization of the Romanowsky staining procedure: an overview

Commerically available Romanowsky blood stains are variable mixtures of thiazein dyes and brominated fluorescein derivatives with varying degrees of metallic salt contamination in a number of different solvent systems. There is a need for standardized Romanowsky stains of constant composition, which, when used in conjunction with a carefully controlled specimen preparation technique, should give consistent performance. Such a preparation system would be of great value to hematologists in general and would be essential to the validity of data obtained by the digital processing of blood cell images. It is possible to prepare standardized Romanowsky stains as mixtures of two or three dye components, namely, eosin Y, azure B and methylene blue, although azure B has only recently become commercially available at an acceptable degree of purity. The logistic problems of stain standardization are discussed.