ACW Lee

Abstract

Examination of the peripheral blood smear is probably an under-utilised laboratory investigation in clinical practice. Three illustrative cases are presented in which reading of the blood smear provides important clues that directly lead to the identification of the infective agents. In the first case, a male neonate with thrombocytopenia at birth manifested polymorphic atypical lymphocytosis. Perinatal cytomegalovirus infection was suspected and was confirmed when the viral DNA was detectable in the plasma. In the second case, a 7-month-old girl was admitted with respiratory distress and signs of pneumonitis. Lymphocytosis with atypical cells showing convoluted nucleus strongly indicated pertussis, which was confirmed when Bordetella pertussis DNA was found from the nasopharyngeal swab. In the third case of a 16-year-old boy who presented with a 3-month history of fever and diarrhoea, the finding of atypical lymphocytosis with abundant large granular lymphocytes pointed to the diagnosis of infectious mononucleosis. This was confirmed when Epstein-Barr virus DNA was found in the plasma. With appropriate management, all recovered from their primary symptoms/signs. Examination of the peripheral blood smear can be a powerful adjunct to guide diagnostic tests and to refine the use of antibiotics in the management of childhood infections.