Fever of unknown origin (FUO) is defined as temperature > 38.3℃ (101°F) on several occasions duration of fever of more than 3 weeks and failure to reach to diagnosis despite one week of inpatient investigations. In general, the causes of FUO have been grouped into four categories: infection or inflammation, non-infectious inflammatory disease, malignancies and miscellaneous. The age, geographic factors, physician’s experience, diagnosis methods, and the developmental status of the country could influence the spectrum of FUO. Infection is the most common cause of FUO, but the high percentage of cases with collagen disease, neoplasm in recent studies suggests the need to be aware of these likely causes of FUO.

In FUO, there is no diagnostic gold standard, and the final diagnoses are determined in a number of ways, including a comprehensive history, physical examination, laboratory tests, anatomical imaging modalities, and a nuclear medicine imaging. Positron emission tomography (PET) is a nuclear medicine imaging technique that detects pairs of gamma rays emitted by a positron-emitting radionuclide, which is introduced into the body on a biologically active molecule. It may detect biochemical changes in a tissue that can identify the onset of a disease process, and then has been successfully used to evaluate different malignant tumors. Positron emission tomography–computed tomography (PET-CT) is able to perform fusion of functional PET and anatomical CT images. In the diagnosis of FUO, Whole-body screening PET is used to provide the detailed metabolic and functional information of the foci while PET-CT offers more definitive anatomic and morphologic information. 

Several recent studies suggest that it will probably become the preferred diagnostic procedure, when a definite diagnosis cannot easily be achieved. However, the diagnostic accuracy of FDG PET/PET-CT in patients with FUO has varied across studies. Thus, this study aimed to perform a systematic review and meta-analysis to examine the overall diagnostic performance of FDG-PET/PET CT in identifying the causal source of FUO.