Preliminary Evaluation of Acridine Orange as a Vital Stain for Automated Differential Leukocyte Counts

Acridine orange in dilute aqueous solution is used as a vital stain to distinguish and differentiate three populations of leukocytes from all other formed elements of the blood. Counts of the first and third of these populations with an automated cytofluorometer correlate well with manual lymphocyte and granulocyte counts on Wright-Giemsa-stained smears. Counts of the second population are systematically higher than manual counts of monocytes, for reasons that are discussed. Reproducibility is much better for the automated differential counts of cells stained with acridine orange than for manual counts of Wright-Giemsa-stained smears. Staining with acridine orange is simple, requiring no hemolysis, and automated counting rates of 100 to 1,000 cells per second are sufficiently fast to accommodate large numbers of specimens in a reasonable period of time.