Axillary Temperature Measurement: Clinical Utility and Limitations
Axillary (armpit) temperature measurement is unreliable and should not guide clinical decisions in either pediatric or adult patients, as it consistently underestimates core temperature by 1.5-1.9°C and shows unacceptable variability that can miss fever or hypothermia. 1, 2
How Axillary Temperature is Measured
- The thermometer is placed in the center of the armpit with the arm held firmly against the body until the device signals completion (typically 30-60 seconds with digital thermometers) 3
- The measurement site can be disturbed by external temperatures, local blood flow, and incorrect placement 1
Critical Limitations in Clinical Practice
Axillary measurements are among the least accurate temperature monitoring methods available:
- Consistently underestimate core temperature by 1.5-1.9°C compared to tympanic measurements 1
- Show variability up to almost 1°C, making them unreliable for detecting true fever or hypothermia 1
- The mean difference increases with rising temperature—only 0.4°C at low temperatures but exceeds 1°C when fever reaches 39°C 4
- Temperature discrepancies of 1-2 degrees from actual core body temperature can lead to missed diagnoses with mortality implications 2, 5
Performance Characteristics in Pediatrics
While some older studies suggested axillary measurements might be acceptable, more rigorous evaluation reveals significant problems:
- In febrile infants, axillary readings are always lower than rectal ones, with limits of agreement ranging from 0.32 to 1.98°C and a mean bias of 1.15°C 6
- Sensitivity for detecting fever is only 46% when using electronic thermometers, meaning more than half of febrile children will be missed 7
- Specificity is high (99%), but the poor sensitivity makes axillary measurement inadequate for clinical decision-making 7
- At best, axillary measurements may be used for screening, but any abnormal reading must be confirmed with rectal or oral measurement 6
Guideline Recommendations
The Society of Critical Care Medicine explicitly recommends against using axillary measurements in critical care settings due to their unreliability 2, 5
- Axillary measurements are categorized alongside no-touch infrared thermometers and chemical dot thermometers as unreliable methods that should not guide clinical decisions 2, 5
- If neither central thermometry nor oral/rectal measurements are feasible, any temperature obtained from axillary methods is unreliable and clinical assessment based on other signs of infection becomes paramount rather than relying on the temperature value itself 2
Preferred Alternatives by Patient Population
For adults and cooperative children (≥4 years):
- Use oral temperature as the most accurate peripheral method (bias of only -0.15°C compared to core temperature) 5
- Ensure patient has not consumed hot/cold fluids for 15-30 minutes and can maintain mouth closure 5
For infants and young children (<4 years):
- Rectal temperature is the gold standard, providing the closest approximation to core body temperature 8
- Normal rectal range is 36.7-37.9°C, with fever defined as ≥38.0°C (100.4°F) 8
For critically ill patients requiring precise temperature monitoring:
- Use central methods: pulmonary artery catheter thermistors, bladder catheter thermistors, or esophageal thermistors 5
- These provide the reference standard with excellent accuracy (bias of only -0.15°C with precision of ±0.13°C) 5
Common Pitfalls to Avoid
- Never rely on axillary temperature alone for critical clinical decisions such as diagnosing serious bacterial infection, sepsis, or hypothermia 2, 5, 7
- Do not assume convenience equals accuracy—the ease of axillary measurement does not compensate for its poor performance 7
- Missing life-threatening infections due to falsely reassuring axillary readings that underestimate true fever 2, 7
- In pediatric emergency settings, axillary temperatures with electronic thermometers should be abandoned in favor of oral or rectal measurements 7