Health article

Sputum Culture: MedlinePlus Medical Test

What is a sputum culture?

A sputum culture is a test that checks for bacteria or another type of organism that may be causing an infection in your lungs or the airways leading to the lungs. Sputum, also known as phlegm, is a thick type of mucus made in your lungs. If you have an infection or chronic illness affecting the lungs or airways, it can make you cough up sputum.

Sputum is not the same as spit or saliva. Sputum contains cells from the immune system that help fight the bacteria, fungi, or other foreign substances in your lungs or airways. The thickness of sputum helps trap the foreign material. This allows cilia (tiny hairs) in the airways to push it through the mouth and be coughed out.

Sputum can be one of several different colors. The colors can help identify the type of infection you may have or if a chronic illness has become worse:

  • Clear. This usually means no disease is present, but large amounts of clear sputum may be a sign of lung disease.
  • White or gray. This may also be normal, but increased amounts may mean lung disease.
  • Dark yellow or green. This often means a bacterial infection, such as pneumonia. Yellowish-green sputum is also common in people with cystic fibrosis. Cystic fibrosis is an inherited disease that causes mucus to build up in the lungs and other organs.
  • Brown. This often shows up in people who smoke. It is also a common sign of black lung disease. Black lung disease is a serious condition that can happen if you have long-term exposure to coal dust.
  • Pink. This may be a sign of pulmonary edema, a condition in which excess fluid builds up in the lungs. Pulmonary edema is common in people with congestive heart failure.
  • Red. This may be an early sign of lung cancer. It may also be a sign of a pulmonary embolism, a life-threatening condition in which a blood clot from a leg or other part of the body breaks loose and travels to the lungs. If you are coughing up red or bloody sputum, call 911 or seek immediate medical attention.

Other names: respiratory culture, bacterial sputum culture, routine sputum culture

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