What criteria should I use to decide whether to refer a patient with acute bronchitis for further investigation?

Refer or seek specialist advice for further investigations in a patient with acute bronchitis if they have symptoms or signs suggesting a more serious condition such as sepsis, pulmonary embolism, lung cancer, or pneumonia. This includes clinical features like respiratory rate over 30 breaths per minute, tachycardia over 130 beats per minute, systolic blood pressure less than 90 mmHg, oxygen saturation below 92% (without chronic hypoxia), altered level of consciousness, use of accessory muscles of respiration, or signs of foreign body aspiration. Also consider referral if symptoms worsen rapidly or significantly, do not improve after 3–4 weeks, or the patient becomes systemically very unwell. Patients with comorbidities (e.g., heart, lung, kidney, liver, neuromuscular disease, immunosuppression, cystic fibrosis), older age with additional risk factors, or those who have already received antibiotics and have worsening symptoms should be considered for specialist advice. If an adequate assessment cannot be made remotely, or if the patient has frailty or immunosuppression, arrange face-to-face assessment and consider referral. Use clinical judgement and risk scores (e.g., CRB65 if pneumonia is suspected) to guide urgency of referral. Routine follow-up is not necessary unless symptoms deteriorate or serious illness is suspected.