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Drugs and diseases reference index

Diseases reference index «Routine sputum culture»

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.

How the Test is Performed

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.

How to Prepare for the Test

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

How the Test Will Feel

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.

Why the Test is Performed

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

Normal Results

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

What Abnormal Results Mean

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.

Alternative Names

Sputum culture