Fever, there are many mysteries surrounding this symptom, but what we do know for sure is that all mammals, some birds, and even a few invertebrate and plant species experience fever’s heat. Fever has persisted for over 600 million years of evolution, but it comes with a significant cost.

For every 1-degree Celsius increase in body temperature, there’s a 12.5% increase in energy required, equivalent to about 20 minutes of jogging for some people.

So, why and how does your body produce a fever? Let’s learn!

Fever In a Nutshell!

Your core temperature is maintained via thermoregulation, a set of processes that usually keep you around 37 degrees Celsius. These mechanisms are controlled by the brain’s hypothalamus, which detects minute temperature shifts and sends signals throughout the body accordingly.

If you’re too hot, the hypothalamus produces signals that activate your sweat glands or cause your blood vessels to dilate, moving blood closer to the skin’s surface to release heat and cool you off.

Conversely, if you’re too cold, your blood vessels will constrict, and you may start to shiver, generating heat.

Terminology

Fever also referred to as pyrexia is an elevation of body temperature (>37.2°C/98.9°F in the morning and 37.7°C/99.9°F in the evening)

Hyperpyrexia: Temperatures >41.5°C (>106.7°F) that can occur with severe
infections but more commonly occur with CNS hemorrhages, it can lead to serious complications including organ damage

Hyperthermia: An uncontrolled increase in body temperature that exceeds the
body’s ability to lose heat without a change in the hypothalamic set point.
Hyperthermia does not involve pyrogenic molecules.

Pyrogen: Substance that can cause fever, including:

Exogenous pyrogens: derived from outside including:

Microbes or their products
Lipopolysaccharide (LPS) of gram-ve bacteria
Enterotoxin from Gram+ve bacteria

Pyrogenic Cytokines:
Interleukin-1
Interleukin-6
Tumor necrosis factor-alpha (TNF)

Mechanism

When the body experiences certain pathological processes, particularly inflammation or microbial toxins,
chemicals called pyrogens are released.

These pyrogenic cytokines are the ones that increase the core body temperature to a new setpoint by stimulating the hypothalamus.

The hypothalamus triggers two physiological responses to facilitate the fever response:

Heat Conservation

Cutaneous vasoconstriction shunts the blood from the periphery to reduce heat loss, that is also the reason why you feel cold with a fever

Heat Production

Shivering produces heat from muscles, non-shivering thermogenesis in the Liver, and behavioral adjustments by putting on more clothes which increases body temperature by simply reducing heat loss.

Hypothalamic Reset

The mechanism by which the hypothalamic setpoint reset downwards in response to antipyretics or immune response against pyrogens involves:

Peripheral Vasodilation & Sweating
promotes heat loss which in turn lowers the temperature.

Causes

The causes of fever can be broadly categorized into:

Infections: The most common cause of pyrexia, which can include bacterial, viral, fungal, or parasitic infections.

Clots: Blood clots or related issues.

Cancers: Various types of cancer can induce fever.

Autoimmune Diseases: Conditions where the immune system attacks the body.

Miscellaneous: Other causes can include heatstroke, medications, brain lesions, and thyroid storm, among others.

How to Approach

To narrow down the diagnosis, a thorough history and examination are necessary, along with appropriate lab investigations where relevant.

Important Questions to Ask in History

These questions can be broadly divided into two categories:

General Fever-Related Questions:

• Duration of Fever: How long has the fever been present?
  
  
• Timing of Fever: What time of day is the fever more prominent?
  
  
• Character of Fever: Is it continuous, intermittent, or relapsing? Is it accompanied by chills or rigors?
  
  
• Night Sweating: Is there night sweating?
  
  
• Weight Loss: Is there unintentional weight loss?
  
  
• Pain: Is there any pain anywhere?
  
  
• Exposure History: Have there been recent exposures to sick individuals, travel history, animal contacts, or insect bites?
  
  
• Medication Use: Is the patient on any medications that could cause fever or interact with other conditions?

Review of Systems:

Ask relevant questions pertaining to each organ system, moving from head to toe. This is especially important in identifying a possible focus of infection For example:

• Head and Neck: Headache, neck stiffness, eye pain, skin rashes or itching, runny nose, ear pain or discharge.
  
  
• Respiratory System: Coughing, sputum production, sore throat, pain on swallowing, difficulty breathing, chest pain.
  
  
• Gastrointestinal System: Abdominal pain, change in bowel habits.
  
  
• Lymphatic System: Lymph node enlargement.
  
  
• Genitourinary System: Burning sensation while urinating, discharge from genitals.
  
  
• Musculoskeletal System: Recent injuries, muscle or bone pain.
  
  
• Other: Recent surgery.

Examine the relevant organ system in thorough detail. You mainly need to decide which of the categories the disease belongs to and which organ system is likely affected.

For example:

• Acute fever with a complaint of burning sensation during urination points to an infection of the urinary tract.
  
• Chronic low-grade fever with anemia and weight loss might indicate a hematological cancer

Investigations

After narrowing down your focus during the history and examination by considering probable diseases and excluding unlikely causes, you may advise certain investigations for the patient if needed. Remember, it is good clinical practice to avoid unnecessary investigations.

Common Investigations:

• Complete Blood Count (CBC): The white cell count is typically raised in cases of infection.
  
• Liver Function Test (LFT): To assess the liver’s health and function.
  
• Urine Routine Examination: To check for signs of urinary tract infection or other abnormalities.
  
• Chest X-ray: To evaluate for pneumonia or other respiratory conditions.

Area-Specific Investigations:

Some diseases are more common in certain areas, so consider including specific tests for them. For example:

• PPD Test for Tuberculosis: Especially in areas where TB is prevalent.
  
• Viral Antibodies for Hepatitis: If hepatitis is suspected or common in the region.

Cultures:

In cases of suspected bacterial infection, cultures may be needed to identify the specific pathogen:

• Urine Culture
  
• Sputum Culture
  
• Blood Culture
  
• Pus Culture (if there is a wound or abscess)

Red Flags

Although a multitude of conditions can cause fever, some are more serious than others and require special attention. Always pay special heed to cases of fever with one of the following:

• Neck Stiffness, Low GCS, or Acute Neurological Deficits: These may indicate serious conditions like meningitis or encephalitis.
  
  
• Severe Chest Pain: This could be a sign of pneumonia, pulmonary embolism, or cardiac issues.
  
  
• Rapid Weight Loss: This may suggest a malignancy or chronic infection.
  
  
• Patient with a Toxic Look: Indicates severe infection or sepsis.
  
  
• Respiratory Distress: Suggests conditions like severe pneumonia, bronchitis, or asthma exacerbation.
  
  
• History of Any Recent Surgical Procedure: May indicate post-surgical infection.
  
  
• Patient Who is Immunocompromised: Higher risk of severe infections.
  
  
• High-Risk Behavior, Including Drug Use and Sexual Promiscuity: Increased risk of infections like HIV, hepatitis, and other sexually transmitted infections.
  
  
• History of Travel to an Endemic Area: Raises suspicion for diseases like malaria, dengue, or other tropical infections.
  
  
• No Obvious Cause for Fever within Three Weeks: This condition is known as pyrexia of unknown origin (PUO) and requires an extensive workup.

Management

Rest: Ensure adequate rest to support the body’s recovery.

Hydration: Maintain proper hydration by drinking fluids like water or herbal teas.

Physical Comfort Measures: Using fewer blankets, wearing lighter clothing, and ensuring a comfortable room temperature can help manage fever-related discomfort.

Antipyretic Medications: Over-the-counter medications such as acetaminophen or ibuprofen can help reduce fever and alleviate discomfort. Always follow dosing instructions and consult with a healthcare provider if uncertain. Source: (Mayo Clinic).

Definitive treatment of fever involves addressing the underlying cause. Since most fevers are due to infections, appropriate antimicrobial drugs should be prescribed.


WARNING! Do not use antibiotics without a proper prescription or for a shorter duration than prescribed, as this can lead to antibiotic resistance, making infections harder to treat.

Conclusion

Fever is a natural and often beneficial response to infection or illness, signaling that the body is actively working to combat an underlying issue.

While most fevers can be managed at home with rest, hydration, and over-the-counter medications, it’s important to recognize when professional medical evaluation is necessary, especially in young children or if the fever is unusually high or persistent.

Understanding how to properly manage and monitor a fever ensures that you can respond effectively, safeguarding your health and well-being.