Fever of unknown origin: Clinical significance of the etiology and common inflammatory parameters.

OBJECTIVES: To analyze the fever of unknown origin (FUO) etiology and clinical characteristics and determine the diagnostic value of common inflammatory parameters.

METHODS: A total of 853 patients with classic FUO were prospectively enrolled from January 2014 to May 2021. According to the etiological diagnosis, the patients were divided according to etiology: infectious diseases (n = 430); non-infectious inflammatory diseases [NIIDs] (n = 153); neoplastic diseases (n = 125); miscellaneous diseases (n = 48); and no identifiable etiology (n = 97). The clinical features and common inflammatory parameters were analyzed.

RESULTS: The clinical characteristics and common inflammatory parameters varied among the FUO patients with different etiologies. The tuberculosis T lymphocyte spot test (T-SPOT.TB) and C-reactive protein (CRP) level might be used as indicators to diagnose infections in patients with FUO. Female gender, young age, high white blood cell (WBC) count and percentage of neutrophil percent (NP), high erythrocyte sedimentation rate (ESR), and elevated serum ferritin (SF) level contributed to the diagnosis of NIIDs. Male gender, old age, low hemoglobin (HB) concentration and platelet (PLT) count, and high lactate dehydrogenase (LDH) and SF levels contributed to the diagnosis of neoplastic diseases. Male gender, old age, and low LDH and SF levels contributed to the diagnosis of infectious diseases. The procalcitonin (PCT) and interleukin-6 (IL-6) levels were highest in FUO patients with neoplastic diseases.

CONCLUSIONS: Infectious diseases are the most frequent cause of FUO, followed by NIIDs. The clinical characteristics and common inflammatory markers have significant value in determining the etiology of FUO.