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Fever/ Pyrexia

Fever is an elevation of body temperature above the normal circadian range as the result of a change in the thermoregulatory center located in the anterior hypothalamus

Max normal oral temp in morning is 37.2*C (98.9*F)

Max normal oral temp in evening is 37.7*C (99.9*F)

Rectal temp is 1*F higher

Given these criteria, an a.m. temp >98.9*F or a p.m. temp of > 99.9*F would define fever.

Febrile response is a complex physiological reaction to an illness, involving a cytokine mediated rise in core temp, the generation of acute phase reactants, & the activation of numerous physiologic, endocrinologic and immunologic systems

Pattern of fever

Sustained fever/continuous fever

Typhoid, pneumococcal

Intermittent fever

Pyogenic abcess, malaria

Remitting fever

Viral infections. mycoplasma

Relapsing feverLymphoma, Dangue

Fever – pulse DisparityTyphoid, legionella

Drug fever

Current evidence

Indicates  fever is a primitive immunologic response with long phylogenetic history

Studies show that fever & its direct consequences are adaptations and natural selection

  1. Specifically to fight infections  both by increasing the phagocytic activity—Neutrophils
  2. Optimizing cytotoxic activity of Lymphocytes

Cost of fever

For each 1*C  rise:

  • Increase in 13% O2 consumption
  • Increase in caloric needs
  • Induction of temp infertility in men
  • Accelerate muscular catabolism
  • Antipyretics frequently used without compelling medical reason
  • In most febrile illness there is no evidence that fever is detrimental & that antipyretics offer any benefit

Whom to be treated first ?

  1. Pregnant women— a hypermetabolic state can be dangerous
  2. Children with hx of febrile seizures
  3. Patients who cannot tolerate a rise in intracranial pressure
  4. Physicians should treat fever only when the expected benefit outweigh the possible risks


With >37.2*C the body responds:

  1. Muscle shivering, vasoconstriction & piloerection–chills
  2. Thereby body conserving temp followed by
  3. Vasodilatation, muscle spasm—-sweeting

Exogenic toxins/pyrogens (Bacteria, viruses, parasites)

Endogenic toxins (cytokines, bacterial products IL-1, IL-6, TNF-a)

  1. Both affect on thermosensitive neurons on Hypothalamus
  2. Thereby increasing heat production & decreasing heat loss
  3. Temp rises till the new set point
  4. This info is conveyed by the temp of the blood flowing around hypothalmus
  • The pyrogens trigger synthesis of prostaglandins of group E from arachdonic acid (PGE2) which through cyclic AMP resets the central thermostat
  • NSAIDS/antipyretics inhibit PGE2 thru inhibiting Cyclo-oxigenase pathway
  • Glucosteroids inhibit all pyrogens thru lipo-oxygenase pathway (IL & TNF-a)
  • Cytokines stimulate immune response at 39.5*C
  • They also recruit neutophils & enhance their functions Indicating fever as a positive factor

Diagnostic approach

History taking

Complete physical examination



Complete physical examination

Do not overlook:

  1. Rash or skin nodules
  2. Eyes
  3. Optic fundi
  4. Upper airways
  5. Rectal examination


  • CP with ESR, C-reactive protein
  • Chest radiograph
  • Malaria films, Urinalysis
  • Blood culture, urine culture, faeces culture
  • Sputum RE & Culture
  • Ultrasound exam of abdomen
  • Serological tests for viruses, bacteria, fungus and parasites
  • LFTs, RFTs
  • Blood sugar, CPK, Bone biochemistry
  • ECG/Echocardiogram
  • Biopsies- Liver, bone marrow
  • Immunological tests-  auto-antibodies, PCR, TB serology

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