CD64, also known as FcγRI, is a high-affinity receptor for the Fc fragment of IgG and belongs to the immunoglobulin superfamily. It is primarily expressed on the surface of monocytes, macrophages, dendritic cells, and neutrophils. Under normal conditions, CD64 expression on neutrophils is low, but it rapidly increases within 4-6 hours upon stimulation by bacterial lipopolysaccharides (LPS), cytokines, or other inflammatory mediators. This upregulation makes CD64 a valuable biomarker for diagnosing bacterial infections, sepsis, and other inflammatory conditions. It has higher sensitivity and specificity compared to traditional markers like white blood cell count, C-reactive protein (CRP), and procalcitonin (PCT) for distinguishing bacterial infections from viral infections or non-infectious inflammation. Additionally, CD64 can be used to monitor treatment efficacy, predict postoperative infections, and guide antibiotic therapy.