CD64, also known as FcγRI, is a high-affinity immunoglobulin G (IgG) Fc receptor primarily found on the surface of monocytes, macrophages, and dendritic cells. It plays a crucial role in the immune response by binding to the Fc region of IgG antibodies, mediating processes such as antibody-dependent cellular phagocytosis and the clearance of immune complexes. Under normal conditions, CD64 is minimally expressed on neutrophils, but its expression can significantly increase in response to infections, making it a valuable biomarker for the early diagnosis of infectious diseases, including sepsis. The upregulation of CD64 on neutrophils, often measured as the CD64 index, has been shown to correlate with the presence and severity of bacterial infections, offering a potentially useful tool for clinicians in the diagnosis and management of sepsis. However, it is important to note that CD64 expression can be influenced by various factors, including medications, underlying diseases, and physiological conditions, which may necessitate a comprehensive interpretation of CD64 levels in clinical practice.