Giemsa stain is a standardized mixture of dyes that makes different cell types stand out clearly in a blood smear or thin slice of tissue. This stain is named for the German chemist, Gustav Giemsa, who first developed it for his work in studying the parasite that causes malaria — Plasmodium. In order to ensure that the technician who examines the sample can obtain an accurate reading, the steps of the staining procedure must be standardized as well as the mixture of dyes. Giemsa stain is called a differential stain because it produces different colors depending on what it bonds to, such as cytoplasm or DNA.
The formula for Giemsa stain has been adjusted over time to improve the stability of the dyes and the colors that result. Current standard mixtures include methylene blue, eosin, and sometimes azure B. These dyes are often stored in a dry powdered form and mixed with water just before they are used. If water is present in the dye mixture before it is used, some of the compounds will oxidize and stain incorrectly.
The exact steps of the procedure for using Giemsa stain may vary depending on which organism or cell type the sample is being examined for as well as the composition of the sample itself. A sample that will be stained using the Giemsa stain is usually smeared on, or affixed to, a slide very soon after it is collected. A thin blood smear is generally fixed by being dipped in methanol, while a thick blood smear is simply allowed to dry completely at room temperature. The slide is then soaked in the stain for a set amount of time and then rinsed with water that has a neutral pH. Slides are allowed to air dry before viewing.
Due to the differential staining produced by Giemsa stain,Plasmodium cytoplasm stains light blue while the DNA appears red or purple. Another parasite, Giardia lamblia, is tinted pink-purple except for the DNA, which stains very dark blue. Histoplasma capsulatum, a fungus, is found in its yeast form in human white blood cells and stains dark blue.
This staining process is also helpful in chromosome studies and in visualizing the differences between various blood cells. A chromosome stains very dark blue in some sections and light blue in others. This causes a banding effect that helps geneticists find places where the chromosomes have gone through unusual changes. Red blood cells stain pink, while the granules in mast cells show up as purple specks. White blood cells stain various shades of blue, allowing the different types — basophils, eosinophils, neutrophils, and others — to be distinguished from one another.