Background The National Institute of Clinical Excellence (NICE) traffic light system uses children’s symptoms and signs to categorise acute infections into red, amber and green. To our knowledge, no study has described the proportion of children with acute undifferentiated illness who fall into these categories in primary care, which is important since red and amber children are considered at higher risk of serious illness requiring urgent secondary care assessment.

Aim To estimate the proportion of acutely unwell children presenting to primary care classified by the NICE traffic light system as red, amber or green, and to describe their initial management.

Design and setting Secondary analysis of the Diagnosis of Urinary Tract infection in Young children prospective cohort study.

Method 6797 children under 5 years presenting to 225 general practices with acute undifferentiated illness were retrospectively mapped to the NICE traffic light system by a panel of general practitioners.

Results 6406 (94%) children were classified as NICE red (32%) or amber (62%) with 1.6% red and 0.3%, respectively, referred the same day for hospital assessment; and 46% and 31%, respectively, treated with antibiotics. The remaining 385 (6%) were classified green, with none referred and 27% treated with antibiotics. Results were robust to sensitivity analyses.

Conclusion The majority of children presenting to UK primary care with acute undifferentiated illness meet red or amber NICE traffic light criteria,with only 6% classified as low risk, making it unfit for use in general practice. Research is urgently needed to establish as triage system suitable for general practice.