What is fever?

A fever is an increase in body temperature above normal in response to an infection, inflammation, drug reactions, or other disease conditions such as cancer and arthritis.

In figure, an oral and rectal temperature measurements of 38ºC and 38.2ºC  respectively or more is fever.

Fever is also called a high temperature, hyperthermia, or pyrexia.
It is a leading cause for seeking medical care globally.

In health, temperature is controlled within limits (in adults at a mean of 36.8C) with diurnal variations of about 0.5C.

Fever is elevation of body temperature that exceeds the normal daily variation and occurs in conjunction with an increase in hypothalamic set point.

In children younger than 5 years of age, fever is:

  • A rectal temperature greater than 38ºC
  • Oral temperature above 37.8ºC
  • Axillary temperature above 37.2ºC

Important points in the history are:

  • Chronology of symptoms
  • Occupational history
  • Travel history
  • Family history
  • Geographic region
  • Physical examination:
    • Vital signs (axillary temperatures are unreliable)
  • Skin, lymph nodes, eyes, nail beds, CNS, chest, abdomen, cardiovascular, musculoskeletal and nervous systems
  • Rectal examination is imperative
  • Pelvic examination (for women)
  • The penis, prostate, scrotum and testes (for men)

Causes of fever

Fever is caused by the following;

  1. Infections
  2. Inflammation
  3. Drugs hypersensitivity
  4. Autoimmune diseases
  5. Cancer
  6. Allergy


The number of investigations will depend on the clinical circumstances.

On occasions, patients may need to be extensively investigated.

1. General:

  • Full Blood Count
  • Differential white blood cell count
  • Urinalysis with examination of the urinary sediment
  • Examination of any abnormal fluid collection

2. Microbiology:

  • Smears and culture of specimens from the throat, urethra, anus, cervix, and vagina (as indicated)
  • Sputum smears; culture
  • Blood culture
  • Urine microscopy, culture and sensitivity
  • Cerebrospinal fluid examination
  • Abnormal fluid collection: specimens for microscopy, culture and sensitivity testing

3. Chemistry:

  • Urine examination
  • Serum urea, electrolytes and creatinine
  • Blood glucose
  • Liver function tests
  • Cerebrospinal fluid examination

4. Radiology:

  • Chest radiograph

Other investigations as may be indicated in the clinical circumstances

Complications of fever

Untreated or poorly treated fever may result in any of the following complications:

  • Heat stroke in adults
  • Febrile convulsions in children
  • Complications associated with underlying cause(s) of fever

Treatment for fever


  • To lower the temperature
  • To treat underlying causes
  • To improve patient’s quality of life

Non-drug treatment

  • Tepid sponging
  • Liberal oral sips of water (if clinical state is not a contraindication)

Drug treatment

1. Paracetamol


  • 500mg – 1 g orally every 4 – 6 hours; maximum 4 g daily


  • 3 months – 1 year: 60-125 mg;
  • 1-5 years: 120 – 250 mg;
  • 6 – 12 years: 250-500 mg; repeated every 4-6 hours if necessary to a maximum of 4 doses in 24 hours
  • Infants under 3 months should not be given paracetamol unless advised by a doctor

2. Aspirin: (acetylsalicylic acid)


  • 300 – 900 mg orally (with or without food) every 4 – 6 hours if necessary; maximum 4g daily


  • under 16 years: aspirin is not recommended in children under the age of 16 because of the risk of Reye’s syndrome. Use paracetamol instead.

3. Treat the identified (or suspected) cause of fever

Notable adverse drug reactions, caution

1. Paracetamol:

  • Liver damage (and less frequently, renal damage) following over dosage

2. Aspirin

  • Gastrointestinal discomfort, nausea
  • Hearing disturbances such as tinnitus (rarely deafness)
  • Ulceration with occult bleeding

Use with caution in the following clinical conditions:

  • Breastfeeding
  • Asthma
  • Allergic disease
  • Impaired renal or hepatic function
  • Pregnancy
  • Elderly
  • Dehydration

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