In almost every Out patient department or a clinic often a febrile illness (fever) without an initially obvious etiology (sometimes called fever without localizing signs) as fever of unknown origin (FUO).
Defining this is based upon simple conditions:
- Fever higher than 38.3ºC on several occasions.
- Duration of fever for at least three weeks
- Uncertain diagnosis after one week of study in the hospital
Later the classification can be pruned down to specific classification based upon:
●Complete blood count, including differential and platelet count
●Blood cultures (three sets drawn from different sites with an interval of at least several hours between each set; in cases in which antibiotics are indicated, all blood cultures should be obtained before administering antibiotics)
●Routine blood chemistries, including liver enzymes and bilirubin
●If liver tests are abnormal, hepatitis A, B, and C serologies
●Urinalysis, including microscopic examination, and urine culture or a
The above broadly help us identify the categories such as:
●Connective tissue diseases (eg, vasculitis, rheumatoid arthritis).