Prior to the 1950s, White Blood Cell counts were usually performed manually using the hemocytometer and the 100 cell microscopic differential count was performed using several variants of the Romanowsky stains, (i.e., Wright Giemsa, May Grunwald).
A key milestone was the award of a patent to Wallace Coulter for using an electronic method for counting particles. Shortly thereafter, he introduced the first viable electronic cell counter, the model A.
With the introduction of the transistor, this led to later models of cell counters, model FN and model S. The model S was the first automated analyzer providing a 7 parameter CBC result. Replacing manual dilutions and counts reduced the turn-around time to one minute from about 15 minutes.
In the early 1970s, Technicon Instruments introduced the Hemalog D, a 5-part differential analyzer based on cytochemistry staining of the WBC subpopulations while analyzing them with a continuous flow, optical measurement system.
Different technical approaches were taken by multiple manufacturers that produced 3, 5, and 6-part differential results.
As the need to reduce the number of manual differentials continued to drive the development of the automated differential, improvements were being made to develop computer based automated digital morphology analyzers. These systems used primitive software to characterize WBC images from a Wright stained smear and provide an estimate of each cell classification, providing images for the technologist to confirm by computer screen review. The Geometric
Data Hematrak model 590 was one such early system. In the 1980s, a 6-part differential was fully incorporated in a benchtop CBC analyzer from Technicon, which also incorporated a laser for light scatter detection.
The Abbott CELL-DYN 4000 was introduced in 1996, with capability for automated enumeration of NRBCs, automated reticulocyte counts, and later introduced automated monoclonal antibody assays for CD61 immuno-platelet count as well as Lymphocyte subsets.
Over the past 20 years, there has been continuous iterations of technological improvements and new methods providing an even more reliable means of reporting an automated differential.