The lymphoid leukocytoses.

The experienced morphologist can be extremely helpful to the clinician by virtue of his or her ability to distinguish among the various subtypes of reactive lymphocytoses. An awareness on the part of the clinician as to the nuances of subclassification may lead to earlier diagnosis of a disease process. Broadly, proliferations of normal lymphocytes point to infectious lymphocytosis or Bordetella pertussis infection. Proliferations of atypical lymphocytes, especially when minimum diagnostic criteria are present or there are four or more Downey III forms per 100 WBCs, suggest infectious mononucleosis. Proliferations of immunoblasts reflect hypersensitivity reactions to drugs or autoimmune disease. Proliferations of proplasmacytes or plasma cells favor viral hepatitis, drug reactions (notably to sulfa drugs), or rubella. Quantitative data may help refine the morphologic implications. Cumulatively, qualitative and quantitative data should lead the clinician to a judicious selection of confirmatory serologic tests and hence to earlier diagnosis.