Every paediatrician and parent recognises the association between fever and rapid respiration rate in children, yet most criteria for judging whether a child is tachypnoeic fail to take temperature into account. In the linked article (doi:10.1136/bmj.e4224), Nijman and colleagues describe respiratory rate reference values that have been adjusted for both temperature and age. Such reference values have the potential to identify lower respiratory tract infection more accurately than traditional ones.1

The World Health Organization recently published data showing that pneumonia was the principal infectious cause of death globally in children under the age of 5 years.2 However, accurate diagnosis can pose a challenge because many children present with respiratory symptoms or acute febrile illness in the absence of identifiable lower respiratory tract infection. One of the most fundamental aspects of assessing a sick child is the measurement of vital signs, but interpreting the findings in the context of a dynamic illness is not straightforward.

Respiratory rates greater than absolute threshold values have been incorporated into many acute care guidelines such …