Visible wavelength light is passed through the sample stream in even the simplest modern hematology analyzers. In most cell counters, the resulting light scatter is used to classify cells by granularity. Visible wavelength light is also used to improve counting of platelets, which are difficult to count because of their variable size and tendency to aggregate. In more sophisticated analyzers, dual angle optical scatter analysis combines optical signals from two independent light sources, eliminating common interferences in platelet counting. In the case of the Abbot CELL-DYNE Sapphire, the dual angle optical platelet count is then validated internally by an impedance count to identify possible interferences.
Newer technologies are incorporated in the more sophisticated cell counter models, improving the accuracy of the automated WBC differential count and enabling further classification of atypical or immature cells. Some hematology analyzers now use flow cytometry labels, lasers, and detectors to distinguish cell populations. This powerful technique classifies immature or atypical cells, which can have deceptively similar appearance in stained blood films, based upon known cell-surface markers. Because the number of cells counted by an automated system is many times greater than the number countable by eye in a manual differential, and because of the specificity of the cell-surface marker labels, the automated cell differential maximizes accuracy in hematology analysis.
A variety of other innovations in hematology analyzers include automated multi-sample loading, closed-tube sampling, barcode sample identification, automated preparation of stained or unstained blood smears, and a variety of data management and reporting systems. Analyzer