Romanowsky stain

Romanowsky staining, also known as Romanowsky–Giemsa staining, is a prototypical staining technique that was the forerunner of several distinct but similar stains widely used in hematology (the study of blood) and cytopathology (the study of diseased cells). Romanowsky-type stains are used to differentiate cells for microscopic examination in pathological specimens, especially blood and bone marrow films, and to detect parasites such as malaria within the blood. Stains that are related to or derived from the Romanowsky-type stains include Giemsa, Jenner, Wright, Field, May–Grünwald and Leishman stains. The staining technique is named after the Russian physician Dmitri Leonidovich Romanowsky (1861–1921), who was one of the first to recognize its potential for use as a blood stain. The value of Romanowsky staining lies in its ability to produce a wide range of hues, allowing cellular components to be easily differentiated. This phenomenon is referred to as the Romanowsky effect, or more generally as metachromasia. In 1891 Romanowsky developed a stain using a mixture of eosin (typically eosin Y) and aged solutions of methylene blue that formed hues unattributable to the staining components alone: distinctive shades of purple in the chromatin of the cell nucleus and within granules in the cytoplasm of some white blood cells. This became known as the Romanowsky or Romanowsky-Giemsa effect. Eosin and pure methylene blue alone (or in combination) do not produce the Romanowsky effect, and the active stains which produce the effect are now considered to be azure B and eosin. Romanowsky-type stains can be made from either a combination of pure dyes, or from methylene blue that has been subject to oxidative demethylation, which results in the breakdown of methylene blue into multiple other stains, some of which are necessary to produce the Romanowsky effect. Methylene blue that has undergone this oxidative process is known as "polychromed methylene blue".