Routine sputum culture

Alternative names
Sputum culture

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
You are 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 medium under conditions that allow the organisms to grow.

How to prepare for the test
Increasing the amount of fluids the night before the test may help to get the sample.

For infants and children:
The preparation you can provide for this test depends on your child’s age and experience. For specific information regarding how you can prepare your child, see the following topics:

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

Why the test is performed
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

What the risks are

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.

Johns Hopkins patient information

Last revised: December 3, 2012
by Gevorg A. Poghosian, Ph.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.