From the Guidelines
Fever does follow a circadian rhythm, with body temperature naturally fluctuating throughout the day, typically being lowest in the early morning and highest in the late afternoon or early evening. This pattern is supported by the most recent evidence from the Society of Critical Care Medicine and the Infectious Diseases Society of America guidelines for evaluating new fever in adult patients in the ICU 1. According to this guideline, the normal body temperature range is subject to various factors, including diurnal variation, which indicates that body temperature varies throughout the day.
Key Points to Consider
- The normal circadian pattern of body temperature is preserved but shifted upward during fever, meaning fever tends to peak in the late afternoon or evening 1.
- The circadian nature of fever is regulated by the body's central circadian clock in the hypothalamus, which controls many physiological processes, including temperature regulation.
- For accurate fever assessment, it's best to measure temperature at consistent times throughout the day, particularly in the late afternoon or early evening when fever typically reaches its highest point.
- Understanding this pattern can help healthcare providers better interpret temperature readings and avoid missing significant fevers by taking measurements only in the morning when body temperature is naturally lower.
Clinical Implications
- The absence of fever in patients with infection is associated with worse outcomes, highlighting the importance of considering other symptoms and signs of infection in the absence of fever 1.
- The definition of fever can vary depending on the context, with different organizations providing different definitions, such as the United States Centers for Disease Control and Prevention and the Infectious Diseases Society of America 1.
- Healthcare providers should be aware of these variations and consider the individual patient's context when evaluating fever.
Monitoring Fever
- Measuring temperature at consistent times throughout the day, particularly in the late afternoon or early evening, is crucial for accurate fever assessment.
- This approach can help healthcare providers capture the peak fever and make informed decisions about patient care.
- The use of consistent temperature measurement times can also help reduce the risk of missing significant fevers and improve patient outcomes.
From the Research
Circadian Variation of Fever
- Fever, or pyrexia, is a physiological mechanism that has beneficial effects in fighting infection 2, 3, 4, 5.
- Normal body temperature values are distributed in a Gaussian manner and are subject to circadian variation, with higher values at night and lower ones during early morning 2, 4, 5.
- The circadian rhythm of body temperature is preserved during malarial fever, with a low around 6 a.m. and a peak about 12 hours later 5.
- Components of acute phase response, including fever, have circadian rhythmicity, but asynchronically 4.
- Fever develops when cytokines increase the thermostatic set point in the hypothalamus, which in turn results in increased body temperature via increased heat production and decreased heat dissipation 2.
Studies on Circadian Variation of Fever
- A study on songbirds found pronounced circadian variation in the body temperature response to lipopolysaccharide (LPS) injection, manifested by hypothermia during the day but fever at night 3.
- A study on humans found that temperature curves showed statistically significant circadian rhythms, with higher values at night and lower ones during early morning 4.
- A study on children with Plasmodium falciparum malaria found that even at febrile temperatures, the temperature followed a clear circadian rhythm 5.