There are no routine tests to diagnose acute bronchitis. Diagnosis is usually based on your medical history, including your symptoms, and a physical examination. Your health professional will make sure you do not have pneumonia or risk factors for more serious diseases, such as chronic obstructive pulmonary disease (COPD), that may affect treatment.

If your health professional feels that your acute bronchitis is caused by:

• A virus, then no more testing is needed in most cases.
• Bacteria, then more testing may be done and antibiotics may be prescribed.

More testing may be necessary for infants and people older than 65, or if:

• Acute bronchitis does not clear up in 2 to 3 weeks.
• Pneumonia, heart failure, or tuberculosis is suspected or has been recently diagnosed.
• Your immune system is not functioning well (impaired immune system). People with immune problems are more likely to develop complications, such as pneumonia.
• You have a chronic respiratory disease, such as asthma or chronic obstructive pulmonary disease (COPD).
• You do not get better with antibiotic therapy, or you require hospitalization.
• You have a heart rate greater than 100 beats per minute, a respiratory rate greater than 24 breaths per minute, and a fever greater than 100.4 F.
• Whooping cough, a bacterial infection of the upper respiratory system, is suspected.
• Influenza (flu), a viral upper respiratory illness, is suspected.

Sometimes other tests may be needed. Possible tests include:

• Chest X-ray. The result of a chest X-ray of people who have acute bronchitis is usually normal.
• Gram stain and culture and sensitivity of the mucus from the lungs. These tests may help determine if bacteria are causing the infection and which antibiotic will be effective.
• Other tests, including tests to measure blood oxygen levels. These tests can help identify bacteria and viruses and can determine whether acute bronchitis is seriously harming lung function.