Fever of unknown origin other diagnostic studies

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Synonyms and keywords: febris continua e causa ignota; febris e causa ignota; febris E.C.I.; fever/pyrexia of obscured/undetermined/uncertain/unidentifiable/unknown focus/origin/source; fever/pyrexia without a focus/origin/source; FUO; PUO


Other than laboratory work up some other investigation listed below may be helpful in finding cause of FUO.[1][2]

Other Diagnostic Studies

Lymph Node Biopsy

Lymph node biopsy may be useful when suspecting lymphoma, lymphogranuloma venereum, toxoplasmosis, and Kikuchi disease. Granulomas in lymph node biopsies may indicate a disorder associated with granulomatous inflammation (eg, tuberculosis, sarcoidosis) or lymphoma. The preferred lymph nodes to biopsy are the posterior cervical, epitrochlear, or supraclavicular nodes.

Bone Marrow Biopsy

Bone marrow biopsy may be considered when there are clues for hematologic malignancies.

Naproxen Test

Naproxen test can be used to distinguish neoplastic fever from other etiologies of FUO.

At a dosage of 375 mg twice daily, naproxen demonstrated no antipyretic activity against fever in patients with occult infection. Defervescence within 12 hours occurs in almost all patients with neoplastic fever. The naproxen test is considered positive when there is a rapid or sustained abatement of fever during the 3 days of the trial period. Fever recurs after discontinuation of naproxen in patients with neoplasms.[3]


  1. Mulders-Manders C, Simon A, Bleeker-Rovers C (2015). "Fever of unknown origin". Clin Med (Lond). 15 (3): 280–4. doi:10.7861/clinmedicine.15-3-280. PMC 4953114. PMID 26031980.
  2. Kaya A, Ergul N, Kaya SY, Kilic F, Yilmaz MH, Besirli K; et al. (2013). "The management and the diagnosis of fever of unknown origin". Expert Rev Anti Infect Ther. 11 (8): 805–15. doi:10.1586/14787210.2013.814436. PMID 23977936.
  3. Chang, J. C. (1987-03). "How to differentiate neoplastic fever from infectious fever in patients with cancer: usefulness of the naproxen test". Heart & Lung: The Journal of Critical Care. 16 (2): 122–127. ISSN 0147-9563. PMID 3028981. Check date values in: |date= (help)