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Sputum Culture

Sputum Culture


National Institutes of Health

Sputum is a secretion that is produced in the lungs and the bronchi (tubes that carry the air to the lung). This mucus-like secretion may become infected, bloodstained, or contain abnormal cells that may lead to a diagnosis. Sputum is what comes up with deep coughing.

How the Test is Performed

The patient is asked to cough deeply and spit any sputum in 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 organisms to grow.

Test Preparation

Asking the patient to drink large amounts of water and other fluids the night before the test may help to get the sample.

Effects of the Test on the Patient

The patient 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.

Purpose of Test

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

Normal Values

No presence of disease-causing organisms in the sputum is normal.

What Abnormal Results Mean

The abnormal results will be reported as a positive culture. That means that there is a disease-producing organism found that may help diagnose bronchitis, tuberculosis, a lung abscess, or pneumonia.

Additional 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.

Special Considerations

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

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