Despite all the advances in laboratory medicine, microscopic review of the peripheral blood smear is still highly informative and clinically relevant and remains an indispensable diagnostic tool. In a pediatric hospital, a common and challenging request is the evaluation of a newborn blood smear. This chapter provides an overview of some of the characteristics of a newborn smear and common reactive conditions.

Blood smear evaluation is often performed for three essential reasons: first, to clarify a flagged result such as immature cells or a low platelet count to rule out pseudo-thrombocytopenia from platelet clumping; second, to evaluate the morphology of red blood cells, white blood cells, and platelets; and, third, to confirm morphologic findings identified by lab staff or an instrument [1]. The latter may be requested by a physician due to a clinical suspicion or by members of the laboratory staff for review of an abnormal finding.

Immunodeficiency-associated lymphoproliferative disorders (IA-LPDs) encompass a heterogeneous group of disorders that stem from diverse clinical settings and underlying disorders. These disorders may be benign lymphoproliferations to aggressive lymphomas. The World Health Organization (WHO) broadly classifies IA-LPDs into four groups: posttransplant lymphoproliferative disorders (PTLDs), lymphomas associated with HIV, lymphoproliferations associated with primary immune disorders, and other iatrogenic lymphoproliferative disorders. This chapter focuses on IA-LPDs of primary immune deficiencies seen commonly in the pediatric population, HIV-associated lymphoma, and iatrogenic lymphoproliferations.

Congenital nonimmune hemolytic anemias are disorders of the red blood cells (RBCs) that occur infrequently in children and adults. These disorders can be divided into three categories: disorders affecting RBC metabolism, the RBC membrane, and hemoglobin synthesis. In this chapter, we briefly describe these conditions and the blood smear morphology. Increasing use of ektacytometry, flow cytometry, or the less sensitive osmotic fragility test can help in analyzing RBC membrane disorders. In addition to morphology of RBCs, RBC enzyme and/or genetic testing can be confirmatory for diagnosis.

Neutrophils are known as the first responders at the sites of infection and injury, but their role in thrombosis is also being recognized. Platelets are known to be an important component in maintaining hemostasis and controlling the bleeding at the site of trauma, as well as in immune modulation [1]. Although some conditions are classified as neutrophilic disorders, they also show clinical manifestations associated with platelet dysfunction, or vice versa. For example, Chediak-Higachi disease is commonly known as neutrophil function disorder; however, it has bleeding history due to abnormal lysosome-like structures inside platelets. Similarly, MYH9-related disorders and Hemansky-Pudlak syndrome are associated with macrothrombocytopenia and storage pool defect but also characterized by neutropenia with recurrent infection and impaired cytotoxic activity.