Pyrexia of unknown origin

Last updated: Friday, 28, January, 2011
Causes Appropriate Tests

PUO is defined as undiagnosed fever of more than 3 weeks duration.

Careful and repeated clinical history and examination; FBC, blood film, differential WCC; CRP ; bilirubin, ALP, AST, ALT, GGT, LD.

Bacterial infection, especially

Blood culture (repeated); urine microscopy and culture; faeces - microscopy, culture and antigen detection.


Abscess, especially

  • Intra-abdominal

Ascending cholangitis

See Cholestasis

Urinary tract infection


Typhoid fever


Urine for mycobacteria testing; collect early morning specimens (three).


Fungal infection

Cryptococcal infection

Cryptococcal antigen - blood, CSF, if appropriate.

Protozoal infection


Malaria parasites - blood - repeated thin and thick blood films, if indicated.


Viral infection

Cytomegalovirus infection

HIV infection

Drug fever

Malignancy, especially

FNAB, lesion biopsy; as appropriate. Tumour markers are unreliable as a screening test for occult malignancy.

Renal cell carcinoma

Hepatocellular carcinoma

Disseminated carcinoma

Hodgkin's disease

Lymphoma (non-Hodgkin's)

Atrial myxoma


Connective tissue diseases


Granulomatous hepatitis

See Hepatitis - Granulomatous


Crohn's disease

Familial Mediterranean fever

Clinical diagnosis.

CRP (intermittent elevation); biopsy of appropriate tissue only if clinical features suggest amyloidosis.

Occult haematoma, especially

  • Retroperitoneal haematoma

Factitious fever