Hemophagocytic syndrome (HPS), also known as hemophagocytic syndrome, hemophagocytic lymphohistiocytosis (HLH), hemophagocytic reticulocytosis reticulosis) is a reactive disease of the mononuclear phagocyte system. It belongs to histiocytic proliferative syndrome class II and is divided into 2 subtypes, including primary FHL (familial hemophagocytic lymphohistiocytic hyperplasia, an autosomal recessive disorder) and secondary HLH (infectious-associated hemophagocytic syndrome, IAHS/VAHS; tumor-associated hemophagocytic syndrome, MAHS; macrophage activation syndrome, MAS). Primary FHL was first named by Farguhar and Claireux in 1952. Although the disease was reported in 1939 (when it was called histiocytic myeloid reticulocytosis), the diagnostic criteria for HLH were only proposed by the International Society of Histiocytes in 1991. Currently, HPS is diagnosed according to the 2004 revised criteria of the International Society of Histiocytes if the molecular diagnosis is clear of the presence of familial or known genetic defects (including mutations in PFR1, UNC13D, MUNC13-4, STX11, SH2D1A, and STXBP2) or 5 of the following 8 conditions ① fever of more than 1 week with a peak value of 38.5°C or higher; ② splenomegaly; ③ two- or three-lineage hematocrit reduction (hemoglobin <90 g/L, <1000 g/L in neonates, platelets <1.0×109/L, absolute neutrophil value <1.0×109/L); ④ elevated serum triacylglycerol (≥3 mmol/L) and/or decreased fibrinogen (<1.5 g/L); ⑤ elevated serum ferritin (≥500 μg/L) (6) elevated plasma soluble CD25 (soluble IL-2 receptor) (>2400 U/mL or 2.4×106U/L); (7) decreased or absent natural killer (NK) cell activity; (8) hemophagocytic phenomenon found in bone marrow, spleen, cerebrospinal fluid or lymph nodes, no malignant cells were seen. Other tests that support the diagnosis are: CNS symptoms, elevated transaminases, elevated bilirubin, lactate dehydrogenase >l000 U/L, histological examination of the involved organs suggesting histiocytosis and lymphocytosis. and concomitant hemophagocytic hyperplasia.