BackgroundGeneral practitioners (GPs) decide which patients with fever need referral to the emergency department (ED). Vital signs, clinical rules and gut feeling can influence this critical management decision.Aimto investigate which vital signs are measured by GPs, and whether referral is associated with vital signs, clinical rules, or gut feeling.Design & settingprospective observational study at two out-of-hours GP cooperativesMethodduring two nine-day periods, GPs performed their regular work-up in patients ≥18 y with fever (≥38.0°C). Subsequently, researchers measured missing vital signs for completion of the Systemic Inflammatory Response Syndrome (SIRS) criteria and the quick Sequential Organ Failure Assessment (qSOFA) score. We investigated associations between the number of referrals, positive SIRS/qSOFA scores and GPs’ gut feeling.ResultsGPs measured and recorded all vital signs required for SIRS/qSOFA calculation in 24 of 108 (22.2%) assessed patients and referred 45 (41.7%) to the ED. Higher respiratory rates, temperatures, clinical rules and gut feeling were associated with referral. During 7-day follow-up, 9 (14.3%) of 63 initially not referred patients were admitted to hospital.ConclusionGPs measured and recorded all vital signs for SIRS and qSOFA in 1 in 5 patients with fever and referred half of 63 SIRS positive and almost all of 22 qSOFA positive patients. Some vital signs and gut feeling were associated with referral, but none were consistently present in all referred patients. The vast majority of patients who were not initially referred remained at home during follow-up.