“In patients with acute cough and sputum production suggestive of acute bronchitis, the absence of the following findings reduces the likelihood of pneumonia sufficiently to eliminate the need for a chest radiograph:
(1) heart rate > 100 beats/min;
(2) Respiratory rate > 24 breaths/min;
(3) Oral body temperature of > 38°C; and
(4)Chest examination findings of focal consolidation, egophony, or fremitus.” Chest. 2006 Jan;129(1 Suppl):95S-103S
Also get a CXR when a patient has:
5) Dyspnea, bloody sputum, or rusty sputum color (Am Fam Physician. 2016 Oct 1;94(7):560-565).
Reference / Further Reading
Chest. 2006 Jan;129(1 Suppl):95S-103S. Chronic cough due to acute bronchitis. http://journal.chestnet.org/article/S0012-3692(15)52837-7/fulltext