Introduction: Myeloperoxidase (MPO), a heme-containing peroxidase is found mostly in the lysosomal azurophilic granules in neutrophils. Since the MPO directly associates with the neutrophil phagocytic system, a large number of diseases that associate with inflammation may directly be linked with MPO levels in neutrophils suggesting it as an active disease biomarker. As the present MPO estimation methods are extremely expensive, development of a slide based quantifiable staining method for MPO is a need.

Aim: To develop a simple quantifiable staining method for MPO in neutrophils on peripheral blood smear with varying hemoglobin concentrations.

Method: Total of 107 patients varying hemoglobin concentrations who attended Hematology Clinic at Colombo North Teaching Hospital, Ragama, Sri Lanka were selected and peripheral blood smears of them were initially fixed with cold buffered acetone, stained with 3-3 Di amino benzidine (3, 3 DAB) and, counterstained with Hematoxylin. Finally, Total MPO of each patient was calculated using a modified formula.

Results: The preliminary findings indicate that the higher intensity groups directly correlates with the higher values of the MPO score whereas the lower intensity groups inversely correlate with the Total MPO scores. The proposed reference range for MPO is 57.6 to 68.4. Total MPO: Absolute Neutrophil Count (ANC) Ratio too correlates with the intensities as the same. Accordingly, the proposed reference range for MPO is 16.4 to 31.4. Conclusion: In this study, we proposed reference ranges for Total MPO estimation. Validation of this method to be performed by comparing with other MPO quantification methods.