In order to differentiate between cell structures, the May-Grünwald/Giemsa stain is used (MGG stain). This staining method works by a chemical reaction between stain substances and the biochemical components of the cell. The stain substances are neutral salts which ionize in water and react with ions in the cell. MGG staining is the basis for the FAB classification.
There are no other special examinations as useful as microscopy of MGG-stained blood and bone marrow smears to differentiate between different types of leukemia.
Flow cytometry immunophenotyping
Flow cytometry immunophenotyping is necessary to clarify the origin of the leukemic clone and for adequate characterization of leukemic cells included for later use for MRD diagnostics.
Cytogenetic and molecular genetic examinations
Using genetic technology methods, for example FISH analysis, (fluorescent in situ hybridization) or PCR (polymerase chain reactions), details are revealed of gene material which change places, lacks or changes of chromosomes, and the significance this has for differentiation and growth of leukemia cells. This has an increasing significance for treatment since the methods are very sensitive for the presence of characteristic gene material from leukemia cells. The most important example of this is evidence of BCR-ABL. PCR will identify BCR-ABL regardless of where the gene is located in the genome, and is today the most sensitive method for finding the fusion gene.
The presence of this fusion gene indicates a poor prognosis using normal chemotherapy. The Philadelphia chromosome (which is a shortened chromosome 22) occurs due to a translocation between chromosome 9 and 22, where the fusion gene BCR-ABL is created .