The most commonly used method for analyzing blood cells using light-specific staining initially involves obtaining a preparation as follows:
– Blood is obtained by venipuncture or by pricking the skin with a needle or stylet.
– A drop of blood is placed on a glass slide; a slide or coverslip is placed against the drop, and this coverslip is pulled away, dragging the blood and producing a very thin film of blood cells. A preparation thus obtained is called a smear or spread.
– The film is left to air dry before being stained.
Staining of blood smears
Blood smears are usually stained with complex mixtures of dyes, called Romanovsky-type stains. There are several slightly different recipes, but almost all have in common a basic dye, an acidic dye, and a metachromatic dye.
A common composition of these solutions is a mixture of the dyes methylene blue, azure B, and eosin.
The combination of these dyes and the affinity of cellular structures for each of them or for combinations of these dyes produces characteristic images of the various cells.
Click to review the concepts of acidic and basic dyes on this page and the following ones.
See the Glossary for the definition of metachromasia.
Important: Designations of structures after use in common mixtures of blood dyes:
Basophilic or basophilic structure – shades of blue.
Acidophilic, eosinophilic, or eosinophilic structure – pink/orange color.
Metachromasia – purple.
