Introducing a Rapid and Safe Method for Myeloperoxidase Staining

Background: Myeloperoxidase staining is used to differentiate leukemias since several decades. Despite implementation of flow cytometric, cytogenetic and molecular techniques for identification of leukemic blasts, histochemical stains such as myeloperoxidase stain are persistently used for better classification of leukemias. The myeloperoxidase staining is a time consuming and hazardous procedure. The present report describes a sensitive, rapid and easy method for assessment of peroxidase activity. Materials and Methods: Bone marrow aspiration slides were stained with Dako product: Code number: K3467 containing DAB chromogen (3,3-diaminobenzidine in chromogen solution) and substrate buffer (Imidasole-HCL buffer, PH 7.5 containing hydrogen peroxide and an anti microbial agent) in a rapid procedure taking only ten minutes time. The staining needs no material preparation steps. Neutrophils in the slide are taken as positive control or another normal smear was costained to be used as control. All cases were followed up with flow cytometry and cytogenetic studies. Result: The reaction product of this stain is brown and granular. Promyelocytes and myelocytes are the most strongly staining cells with positive (primary) granules. Lymphoblasts are negative. The result of classification of leukemias with this technique was in concordance with flow cytometric immunophenotyping. Discussion: Many practical techniques have been described using benzidine as an indicator for myeloperoxidase staining. Benzidine is a carcinogenic material and its usage is severely restricted in laboratory. Formerly we prepared requisite materials for myeloperoxidase staining by hazardous ways (boiling), but we decided to apply ready to use 3,3-diaminobenzidine (DAB), which is used in final step of immunohistochemistry stains. Conclusion: Use of 3,3-diaminobenzidine (DAB) is highly recommended for myeloperoxidase staining, while the result is extraordinary and fully compatible with flow cytometry and the method is safe and rapid.