Persistent low-grade fever but normal blood counts may be due to viral infections, tuberculosis infectious fevers, connective tissue disease, and lymphoma. 1. Infectious fever: for example, common viral infections and tuberculosis may lead to prolonged low-grade fever, which mostly manifests itself as persistent low-grade fever and night sweats in the afternoon, and may also have other manifestations such as weight loss. Specialized infections such as brucellosis may also cause prolonged low-grade fever. Blood counts may show no obvious abnormality. 2. Connective tissue disease: connective tissue disease is an autoimmune disease, which may cause persistent low-grade fever, joint pain and other manifestations, and the blood routine may be normal. 3. Lymphoma: Lymphoma is a malignant tumor of the blood system, which can be manifested as persistent low-grade fever or high fever, abnormal blood counts, enlarged liver and spleen, and so on. The above are only some of the common causes. When the patient’s blood routine is normal but persistent low fever, he should consult doctor as soon as possible, and follow the doctor’s instruction to standardize the treatment after clear diagnosis.