-A 15-day-old girl is admitted to the neonatal intensive care unit (NICU) with sepsis. Complete blood count (CBC) indices are: WBC: 12.6 x10^9/L, RBC: 3.36 x10^9/L, Hemoglobin: 10.7 g/L, MCV: 98 fL, MCH: 31 pg, Platelet: 30 x10^9/L, MPV: 8.0 fL

-The peripheral blood smear showed rare histiocytes with hemophagocytic activity.

Comment: The presence of histiocytes in peripheral blood smear is uncommon and should indicate further investigation for primary and secondary causes of hemophagocytic lymphohistiocytosis (HLH). The presence of such cells, however, are not diagnostic of HLH. Other criteria should be met before making a formal clinical diagnosis of HLH as hemophagocytic histiocytes by themselves are not specific for any one entity.

-In the provided case, the most likely cause of the noted circulating hemophagocytic histiocytes is the patient’s severe infection and sepsis.