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For further information, see CMDT Part 2-08: Fever & Hyperthermia

Key Features

Essentials of Diagnosis

  • Inquire about

    • Age; injection substance use

    • Localizing symptoms; weight loss, joint pain

    • Immunosuppression or neutropenia; history of cancer; risk for SARS-CoV-2 infection

    • Medications

    • Travel

General Considerations

  • Fever is a regulated rise to a new "set point" of body temperature mediated by pyrogenic cytokines

  • The fever pattern is of marginal value, except for the relapsing fever of malaria, borreliosis, and lymphoma (especially Hodgkin disease)

  • Fever, with rash and eosinophilia, define the drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome

  • Most febrile illnesses are

    • Due to common infections

    • Short lived

    • Relatively easy to diagnose

  • A normal body temperature based on a peripheral thermometer (tympanic membrane, temporal artery, axillary, oral) does not always exclude the presence of a fever

  • Rectal is more reliable than oral temperature, particularly in patients who breathe through their mouth, who are tachypneic, or who are in an ICU setting where a rectal temperature probe can be placed

  • Fever in the neurointensive care unit

    • Can occur directly from brain injury (so-called "central fever")

    • Following criteria predict "central fever" with 90% probability

      • Occurs < 72 hours after neurologic ICU admission

      • Presence of subarachnoid or intraventricular hemorrhage

      • Brain tumor

      • Absence of infiltrate on chest radiograph

      • Negative cultures

    • Serum procalcitonin and C-reactive protein (CRP) may have some utility in differentiating infectious and central fever in the ICU

Clinical Findings

Symptoms and Signs

  • Fever is defined as an elevated body temperature exceeding 38.3°C

  • The average normal oral body temperature taken in mid morning is 36.7°C (range 36.0–37.4°C)

  • The normal rectal or vaginal temperature is 0.5°C higher; the axillary temperature is 0.5°C lower

  • The normal diurnal temperature variation is 0.5–1.0°C—lowest in the early morning and highest in the evening

  • There is a slight sustained temperature rise following ovulation, during the menstrual cycle, and in the first trimester of pregnancy

  • Spinal cord injury may cause fever by the loss of supraspinal control of the sympathetic nervous system and defective thermoregulation due to loss of sensation

Differential Diagnosis

Common causes

  • Infections

    • Bacterial

    • Viral

    • Rickettsial

    • Fungal

    • Parasitic

  • Autoimmune diseases

  • CNS diseases

    • Head trauma

    • Mass lesions

  • Malignant disease

    • Renal cell carcinoma

    • Primary or metastatic liver cancer

    • Leukemia

    • Lymphoma

  • Cardiovascular diseases

    • Myocardial infarction

    • Thrombophlebitis

    • Pulmonary emboli

  • Gastrointestinal diseases

    • Inflammatory bowel disease

    • Alcoholic hepatitis

    • Granulomatous hepatitis

  • Miscellaneous diseases

    • Drug fever

    • Sarcoidosis

    • Familial Mediterranean fever

    • Tissue injury

    • Hematoma

    • Factitious fever


  • Peripheral thermoregulatory disorders

    • Heat stroke

    • Malignant hyperthermia of anesthesia

    • Malignant neuroleptic syndrome


Laboratory Tests

  • Complete blood count with differential

  • Urinalysis

  • Erythrocyte sedimentation rate (ESR) or C-reactive protein ...

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