Rapid detection of pathognomonic blood cells in patients with infectious mononucleosis.

Veneous blood-citrate samples of patients with infectious mononucleosis were stained with DAPI, a newer fluorochrome (4',6-diamidino-2-phenylindole) to demonstrate the "large atypical lymphocytes" associated with this disease. As a result of the capacity of DAPI to stain DNA and certain acid mucopolysaccharides, a rapid detection of the pathognomonic white blood cells could be achieved. Most of them revealed the well known indented or lobulated nuclei and vacuolated (foamy) cytoplasm. Others exhibited kidney-shaped nuclei, often filled with yellow-fluorescent tiny granula. In our view, the rapid, specific and sensitive DAPI-technique for detecting pathognomonic blood cells in patients with infectious mononucleosis can be considered an improved microscopic method.