The added value of peripheral blood cell morphology in the diagnosis and management of infectious diseases—part 1: basic concepts

As automated blood cell analysers and sophisticated diagnostic technologies become widespread, requests for peripheral blood smear (PBS) examination—for the diagnosis of infectious diseases—diminish. Yet, PBS examination can provide rapid and invaluable information on infection—host susceptibility, aetiology, severity, and systemic impact. Besides direct visualisation of certain microorganisms (for example, Plasmodium , Ehrlichia ), PBS examination may detect characteristic footprints left by various infections on the morphology of blood cells, thus yielding the cytologic clues of the disease (for example, Dohle bodies, haemophagocytosis). Additionally, PBS examination may disclose certain infection predisposing conditions (for example, May–Hegglin anomaly, hyposplenism), and several infection related haematological and systemic complications. Combined with a careful medical history and physical examination data, all this information may yield a speedy diagnosis, a rationalised diagnostic work-up, and timely initiation of treatment. The intention of the following review is to highlight the value of PBS, and recommend that PBS examination should be fostered in the diagnostic work-up of infectious diseases.