Relationships between Causes of Fever of Unknown Origin and Inflammatory Markers: A Multicenter Collaborative Retrospective Study

Objective Although inflammatory markers, such as the white blood cell (WBC) count, erythrocyte sedimentation rate (ESR) and levels of C-reactive protein (CRP) and procalcitonin, are widely used to differentiate causes of fever of unknown origin (FUO), little is known about the usefulness of this approach. We evaluated relationships between the causes of classical FUO and the levels of inflammatory markers. Methods A nationwide retrospective study including 17 hospitals affiliated with the Japanese Society of Hospital General Medicine was conducted. Patients This study included 121 patients ≥18 years old diagnosed with "classical FUO" (axillary temperature ≥38.0°C at least twice over a ≥3-week period without elucidation of the cause on three outpatient visits or during three days of hospitalization) between January and December 2011. Results The causative disease was infectious diseases in 28 patients (23.1%), non-infectious inflammatory disease (NIID) in 37 patients (30.6%), malignancy in 13 patients (10.7%), other in 15 patients (12.4%) and unknown in 28 patients (23.1%). The rate of malignancy was significantly higher for a WBC count of 40 mm/h. A normal ESR appeared to constitute powerful evidence for excluding a diagnosis of malignancy. In contrast, the concentrations of both serum CRP and procalcitonin appeared to be unrelated to the causative disease. Conclusion The present study identified inflammatory markers that should be considered in the differential diagnosis of classical FUO, providing useful information for future diagnosis.