Blood Film Preparation and Staining Procedures
INTERPRETATION OF THE PERIPHERAL 00. ם BLOOD FILM 0272–2712/02 $15.00 BLOOD FILM PREPARATION AND STAINING PROCEDURES Berend Houwen, MD, PhD The blood film is one of the world’s most widely and frequently used tests and has undergone remarkably few changes since its introduction as a clinical diagnostic tool in the late 1800s. The origins of stained blood film microscopy are somewhat obscure, and a clear reference for the ‘‘first person or persons’’ to describe its use as a clinical laboratory procedure cannot be established with certainty. Antonie van Leeuwenhoek, in the seventeenth century, was the first to describe blood cells, using whole blood preparations and not blood films for his observations on blood corpuscles. In fact, he would not have been able to use blood film–based microscopy because it requires considerably more sophisti- cated optics than were available in his day. A second technologic innovation enabling blood film microscopy was the introduction of aniline dyes in the second half of the nineteenth century. This made it possible to study individual blood cells by light microscopy after a small amount of blood had been placed and smeared onto glass slides, dried, fixed, and then stained. Paul Ehrlich introduced eosin as the first of these dyes for staining blood films in 1856, followed by hematoxylin in 1865, and later by the metachromatic Romanowsky dyes. A few refinements have since been made, consisting mainly of improve- ments in dye quality, staining procedures, automation of slide preparation, and staining, but the basic elements of blood film preparation and analysis have not changed for over a century.
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