Laboratory Examination in Hemophagocytic Lymphohistiocytosis

Hemophagocytic Lymphohistiocytosis (HLH) is derived from the word hemophagocytosis, in which macrophagesinfiltrate tissue extensively, and unspecifically phagocyte blood and bone marrow cells. The deviant activation of cytotoxicCD8+ T-cells causing the release of inflammatory cytokines is the core pathogenesis of HLH. Hemophagocyticlymphohistiocytosis is a regulatory disorder of the immune system, with clinical signs and symptoms of extremeinflammation and cytopenia, hepatitis, and severe and life-threatening central nervous system dysfunction. The name of theHLH disorder was recently proposed to be "Hyperinflammatory Lymphohistiocytosis" (also known as HLH). Enforcement ofHLH diagnosis by the Histiocyte Society based on HLH 2004 updated diagnostic criteria consists of five of the following eightdiagnostic criteria: fever, splenomegaly, cytopenia (two or more of three lineages in peripheral blood), hypertriglyceridemiaor hypofibrinogenemia, hyperferritinemia, hemophagocytes in the bone marrow/lien/lymph, the low or non-existentactivity of Natural Killer (NK) cells, increased sCD25. H-score, MH-score, and systemic Juvenile Idiopathic Arthritis(sJIA)/Macrophage Activated Syndrome (MAS) classification criteria are also used to enforce HLH diagnoses.Hemophagocytic lymphohistiocytosis is challenging to recognize and has a high mortality rate, especially in adults, rangingfrom 42 to 88%. Therefore, immediate diagnosis and therapy are essential. The introduction of HLH triggers is criticalbecause treatment is based on the underlying trigger. Cytokine storms due to Coronavirus Disease 19 (COVID-19) infectionhave significant similarities to the clinical and laboratory findings of HLH. Secondary HLH (sHLH) is suspected in severeCOVID-19 patients, so early diagnosis is potentially made based on the H-score.