FUO is defined as the presence of fever of 38.3°C or more recorded on several occasions, evolving for at least 3 weeks with no diagnosis reached even after one week of relevant and intelligent investigations. FUO is usually an uncommon presentation of common diseases.

Salient features:-

Common causes include

  • Infections, particularly extrapulmonary tuberculosis, typical and atypical mycobacterial infections, Pneumocystis carinii pneumonia, toxoplasmosis, lymphoma etc. In neutropenic patients, gram negative bacterial, staphylococcal and fungal infections are important causes

Neoplastic conditions:-

  • Noninfectious inflammatory causes collagen vascular diseases, drug fevers
  • Prolonged unexplained fever, often with no localizing clue on history, physical examination and basic laboratory investigations


  • A detailed clinical history, repeated physical examination to provide potentially diagnostic clues (PDC).
  • No single algorithmic approach to diagnosis can be recommended for all patients of FUO and diagnostic approach needs to be individualized.
  • A complete haemogram including peripheral blood smear for malaria parasite, serum biochemistry particularly liver function tests, a tuberculin test and an X-ray of chest should be done in every patient with prolonged fever.
  • Other investigations which are often helpful include tests related to collagen vascular diseases, an ultrasonography to localize intra-abdominal foci of infections and a contrast enhanced computed tomography (CECT) of chest and abdomen in detecting mediastinal lymph nodes and parenchymal lung abnormalities not seen on conventional chest X-ray.

Further, diagnostic approach should take into consideration the PDCs from the evaluation of history, results of repeated physical examination, basic investigations and any investigations done prior to this episode. If any abnormal or doubtful lesion is detected FNAC/biopsy should be obtained.


Sometimes evaluation may need discontinuation of all drugs being taken by the patient to rule out drug fever as the cause of FUO.

Symptomatic treatment for fever (for details see section on fever)

  • Cold sponging may be done if fever produces discomfort. The emphasis in patients with classic FUO is on continued observation and examination.
  • (Caution: Avoid ‘shotgun’    Empirical  therapies  consisting  of  therapeutic  trials

commonly used in patients with FUO are: antibiotics, anti-tubercular treatment (ATT) and corticosteroids).

  • The ability of glucocorticoids and NSAIDs to mask fever while permitting the spread of infection dictates that their use should be avoided unless infection has been largely ruled out.
  • If on the basis of clinical evaluation and inability to reach a definitive diagnosis, a therapeutic trial is started, the following principles must be kept in mind:
  • Give only one set of trial at a given time
  • The doses of drugs and period of therapeutic trial must be adequate-

The patient must be followed closely for response

Patient education

  • Self medication should be avoided.
  • Antibiotics should be taken only on advice of a physician.

Plenty of fluids should be taken. Stay in a cool environment.

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