Sputum culture Test

What is a sputum culture test?

A sputum culture is a diagnostic test identifying bacteria or other organisms causing lung or airway infections. Sputum, a thick mucus produced in the lungs, contains immune cells that fight against foreign substances. During the test, a sample of sputum is collected and analyzed in the lab using a special culture medium. This helps identify the organisms present and guides treatment decisions.

A sputum culture is typically ordered when a person is experiencing symptoms of a respiratory infection, such as a persistent cough, fever, chest congestion, or difficulty breathing. The test helps doctors diagnose and guide appropriate treatment for respiratory infections, such as pneumonia, bronchitis, or tuberculosis.

Who conducts sputum culture tests?

The sputum culture tests are typically conducted by laboratory technicians in clinical laboratories. They perform the necessary steps for sputum culture tests, such as staining, incubating, and analyzing the collected samples. Pathologists oversee the interpretation of sputum culture findings.

What is it used for?

A sputum culture is commonly used for:

  • Identifying and diagnosing bacteria or fungi that may be causing an infection in the lungs or airways.
  • Assessing the progression or worsening of a chronic lung illness.
  • Monitoring the effectiveness of treatment for an existing infection.


In many sputum culture tests, a complementary procedure called a sputum Gram stain is commonly performed. This technique involves the application of a dye to the sputum sample, which is subsequently examined under a microscope. The visual characteristics of the stained sample aid in classifying the specific bacteria that are present.

Taking the sputum culture test

To do a sputum culture test, enough sputum (thick mucus) is needed. There are two main ways to get sputum samples:

  • Coughing and spitting into a cup: The most common way is to cough deeply and spit the phlegm (thick mucus) into a special cup. This is the easiest and least invasive method.
  • Bronchoscopy: Sometimes, a procedure called bronchoscopy is used. If coughing doesn’t give enough sputum or the initial test results are unclear, a bronchoscopy might be done. During bronchoscopy, a flexible tube with a camera on the end is gently put through the nose or mouth to look inside the lungs. This camera tube might have a brush or tool to collect a sputum sample from the lungs.

In the laboratory, the sputum sample is cultured on specialized media supporting bacteria or fungi growth. The culture allows the microorganisms to grow over a specific period, usually 48 to 72 hours. After sufficient growth, the organisms are identified and tested for susceptibility to specific antibiotics if necessary.

The results of a sputum culture can help determine the type of infection present and guide appropriate antibiotic treatment if needed. It is important to note that the results may take a few days to become available, as the growth and identification of microorganisms require time.

What can we learn from looking at the color of sputum?

The color of sputum can provide valuable information about an individual’s respiratory health. The colors can help identify the type of infection.

Clear: Usually indicates the absence of disease, but large amounts of clear sputum can indicate lung disease.

White or gray: This can be normal, but increased amounts may suggest lung disease.

Dark yellow or green: Often associated with bacterial infections such as pneumonia or common in individuals with cystic fibrosis.

Brown: Frequently seen in smokers and may also indicate black lung disease caused by prolonged exposure to coal dust.

Pink: This may indicate pulmonary edema, a condition characterized by fluid accumulation in the lungs, commonly seen in congestive heart failure patients.

Red: May indicate early signs of lung cancer or a pulmonary embolism, a serious condition where a blood clot travels to the lungs. If the patient coughs up red or bloody sputum, seek immediate medical attention.

It is important to note that sputum color alone cannot provide a definitive diagnosis, and further testing is required.


  1. What is a sputum culture? Available from: https://www.webmd.com/lung/what-is-a-sputum-culture
  2. Sputum Culture. Available from: https://medlineplus.gov/lab-tests/sputum-culture/

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