Prolonged fever without a cause is also known as fever to be investigated. Factors leading to fever include infectious and non-infectious factors, and it is recommended to carry out appropriate tests under the guidance of a doctor to check each one of them. 1. Infectious factors: the cause of fever is pathogenic microbial infections, which should be examined in conjunction with the accompanying symptoms. If accompanied by diarrhea, abdominal pain and other symptoms, routine stool tests should be performed to screen for gastrointestinal infections. If accompanied by cough, shortness of breath, lung imaging, screening for lung disease. If accompanied by frequent urination and other symptoms, need to screen for urinary tract infections. 2. Non-infectious factors: If the fever is caused by a tumor, it is necessary to screen for the primary tumor lesion. If the fever is caused by hematological diseases, bone marrow aspiration is needed. Fever caused by rheumatologic diseases requires autoantibody testing. If the cause of fever cannot be found for a long period of time, it is recommended to actively cooperate with the doctor to carry out a full range of disease screening, and actively carry out treatment after clarifying the cause of the disease, so as to avoid delaying the condition.