The diagnosis of hemophagocytic syndrome (HLH), a rare disease with no specific clinical manifestations, is complicated by its potentially variable systemic disorder. rapid diagnosis of HLH is key to treatment, and NK cell activity, sCD25, phagocytosis phenomenon, ferritin, CD107a, and genetic testing help to make a timely and accurate diagnosis. This article discusses the role of the above-mentioned indicators in the diagnosis of HLH, with the aim of improving the understanding of the value of the above-mentioned laboratory tests in the diagnosis of this disease. Hemophagocytic syndrome (HPS), also known as hemophagocytic lymphohistiocytosis (HLH), is a life-threatening state of excessive inflammatory response caused by multiple factors that lead to excessive proliferation and activation of lymphocytes and histiocytes and the production of large amounts of inflammatory factors. The main clinical manifestations are fever, splenomegaly, holocytopenia, hypertriglyceridemia, hypofibrinogenemia, and hypoferritinemia. HLH is divided into primary and secondary, and primary HLH includes three categories: (i) familial phagocytic syndrome (FHL-1 to FHL-5 types); (ii) immunodeficiency syndrome (GS-2, CHS-1, HPS- II); (iii) EBV-driven associated phagocytic syndrome (XLP-1, XLP-2, IL-2Cinducible T- cell kinase deficiency , CD27 deficiency, XMEN) [3]. Secondary HLH can be caused by a variety of factors, such as infections, autoimmune diseases, malignancies, etc. [4]. In this paper, we discuss the laboratory tests related to HLH. According to the diagnostic criteria of HLH-2004, HLH is diagnosed by the presence of familial or known genetic defects (including mutations in PRFI, UNCl3D, STXll and STXBP2) by molecular biology, or by five of the following eight indicators: (i) fever: >7 days and temperature >38.5°C; (ii) splenomegaly (≥3 cm below the rib cage); (iii) peripheral blood cytopenia (involving two or three lines): HGB <90 g/L, PLT <100 x109/L, neutrophils <1.0 x109/L and not due to bone marrow hypoplasia; ④ elevated triacylglycerol and/or reduced fibrinogen: triacylglycerol >3 mmol/L or 3 standard deviations above the reference value for the same age, fibrinogen/L or 3 standard deviations below the reference value for the same age (5) phagocytes found in the bone marrow, spleen, or lymph nodes; (6) reduced or absent natural killer (NK) cell activity; (7) serum ferritin ≥500ug/L; and (8) elevated soluble IL-2 receptor (slL-2R or sCD25). Unfortunately, there is no specific index for rapid diagnosis of HLH. Janka et al. concluded that: persistent high fever, hepatosplenomegaly and hematocrit should be highly suspected of HLH; Filipovich et al. concluded that: unexplained persistent fever, hepatic impairment, coagulopathy and unexplained hematocrit need to be considered for HLH. obviously, when the above symptoms are present, it is necessary to It is clear that when these symptoms are present, reasonable tests are needed to confirm or exclude the diagnosis of HLH in order to give early and proper treatment.