Routine sputum culture is a test of secretions from the lungs and bronchi (tubes that carry air to the lung) to look for bacteria that cause infection.

Sputum culture

You will cough deeply and spit any sputum into a sterile cup. The sputum is then taken to the laboratory. There, it is placed in a special substance (medium) under conditions that allow the bacteria or fungi to grow.

Drinking a lot of water and other fluids the night before the test may help to get the sample.

You will need to cough. Sometimes the health care provider will tap on the chest to loosen deep sputum. There may be a steam-like mist to inhale to help you cough up the sample.

The culture is done on the sputum to help identify the bacteria that are causing an infection in the lungs or airways (bronchi).

In a normal sputum sample there will be no disease-causing organisms present.

If the sputum sample is abnormal, the results are called "positive." Identifying disease-producing organisms may help diagnose:

• Bronchitis
• Lung abscess
• Pneumonia
• Tuberculosis

Other conditions under which the test may be performed:

• Aspiration pneumonia
• Atypical mycobacterial infection
• Atypical pneumonia
• Blastomycosis
• Bronchiectasis
• Coccidioidomycosis; acute (primary) pulmonary
• Coccidioidomycosis; chronic pulmonary
• Coccidioidomycosis; disseminated
• Cryptococcosis
• Disseminated tuberculosis (infectious)
• Histoplasmosis; acute (primary) pulmonary
• Histoplasmosis; chronic pulmonary
• Hospital-acquired pneumonia
• Mycoplasma pneumonia
• Plague
• Pulmonary aspergilloma (mycetoma)
• Pulmonary aspergillosis; invasive type
• Pulmonary tuberculosis
• Viral pneumonia

There are no risks with this method of obtaining a sample.

Sometimes a gram stain or AFB stain of the sputum done at the same time can help make the diagnosis.