What is the technical cutoff for a fever?

From the Guidelines

The technical cutoff for a fever is generally considered to be a body temperature of 100.4°F (38°C) or higher, as defined by the most recent guidelines from the Society of Critical Care Medicine and the Infectious Diseases Society of America 1. This threshold applies when temperature is measured orally in adults. However, normal body temperature can vary slightly from person to person and fluctuates throughout the day, typically being lowest in the early morning and highest in late afternoon. The measurement method also affects the reading - rectal temperatures run about 0.5-1°F higher than oral temperatures, while armpit (axillary) temperatures tend to be 0.5-1°F lower than oral readings. For infants and young children, doctors often use different thresholds, sometimes considering 100.4°F rectally as the fever cutoff, as noted in guidelines for evaluating new fever in adult patients in the ICU 1 and for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months 1. Fever itself is not an illness but rather a symptom of an underlying condition, typically representing the body's natural defense mechanism against infection. The elevated temperature helps the immune system fight pathogens more effectively by creating an environment less favorable for bacterial and viral replication while accelerating the body's immune responses. Some key points to consider include:

• The definition of fever can vary depending on the context and population, with some guidelines using a cutoff of 38.3°C (101°F) for neutropenic patients 1 or 38.5°C for symptomatic treatment of fever in patients with 2019 novel coronavirus infected pneumonia 1.
• The absence of fever does not rule out infection, and some patients with serious infections may be hypothermic or euthermic 1.
• The use of antipyretic agents can affect the presentation of fever and should be considered when evaluating patients with suspected infection 1. Overall, the technical cutoff for a fever is an important consideration in clinical practice, and healthcare providers should be aware of the different definitions and thresholds used in various guidelines and populations.

From the Research

Definition of Fever

• Fever is defined as an increase in body temperature above what is considered to be a normal value 2.
• The normal body temperature is typically considered to be around 98.6°F (37°C), but it can vary slightly from person to person.

Technical Cutoff for Fever

• There is no specific technical cutoff for fever mentioned in the provided studies.
• However, one study mentions that most respondents chose a temperature of 101°F to start antipyretic treatment 3.
• Another study mentions that 57% of respondents used ibuprofen for temperature ≥102 degrees F 3.

Fever Measurement and Assessment

• Measurement of body temperature remains one of the most common ways to assess health 2.
• Fever is often accompanied by various sickness behaviors, changes in metabolic and physiological characteristics of body systems, and alterations in immune responses 4.

Antipyretic Treatment

• Antipyretic drugs are routinely administered to febrile patients with infection in secondary care 5.
• The use of antipyretics to suppress fever during infection remains a controversial topic within the literature 5.
• Some studies have demonstrated improved patient outcomes following antipyretic administration, while others have demonstrated increased mortality risk associated with antipyretics 5, 6.