Crocker ME, Hossen S, Goodman D, et al. - A cross-sectional study was performed to ascertain upper thresholds for respiratory rate (RR) and lower thresholds for oxyhaemoglobin saturation (SpO2) by age and altitude at four sites, with altitudes ranging from sea level to 4,348 m. Researchers included healthy children aged 0–23 months who lived within the study areas in India, Guatemala, Rwanda, and Peru. This study screened 2,027 children for eligibility between Nov 24, 2017, and Oct 10, 2018 (335 were ineligible, leaving 1,692 eligible individuals). Because of missing values, 30 children were excluded and 92 were excluded because of measurement or data entry errors, leaving 1,570 children in the final analysis. For fast breathing and hypoxaemia, WHO cutoffs overlap with RR and SpO2 values that are normal for children at different altitudes. In many children, the use of WHO definitions for fast breathing could occur in misclassification of pneumonia who live at moderate to high altitudes and display acute respiratory signs. In all regions except for Peru, the 5th percentile for SpO2 was in reasonable agreement with the WHO definition of hypoxaemia. It was noted misclassifications could appear in inappropriate management of paediatric respiratory illness and misdirection of potentially scarce resources such as antibiotics and supplemental oxygen. Further research at various altitudes is required to confirm the findings and suggest a revision to current guidelines.