MayGrÄnwald

May-Grünwald, often written May-Grünwald stain, is a cytological stain used to differentiate cellular components in fixed blood and bone marrow smears. It was developed in the early 20th century by Rudolf May and Gustav Grünwald and remains widely employed in hematology and cytology. The stain is commonly used as part of the May-Grünwald–Giemsa (MGG) procedure, a two-step protocol that enhances color contrast and supports reliable morphological assessment of blood cells and bone marrow specimens.

In the May-Grünwald step, a methanol-fixed smear is treated with a dye solution containing blue and red chromogens, resulting in nuclei that stain blue to purple and cytoplasm that ranges from pale pink to violet depending on cell type. The subsequent Giemsa step provides further differential staining of cytoplasmic granules and surrounding structures, producing a characteristic morphology that aids in the identification of leukocyte lineages, maturation stages, and various hematologic abnormalities. The combined approach, MGG, is valued for clear nuclear detail, good cytoplasmic differentiation, and broad applicability to routine morphology.

Applications include peripheral blood analysis, bone marrow examination, and other hematologic specimens. The stain is considered cost-effective and relatively straightforward, making it a standard option in many laboratories for routine differential counts and Morphologic assessments. While many labs continue to use the May-Grünwald–Giemsa combination, some practitioners employ the May-Grünwald stain alone for basic cytology and preliminary evaluation.