Routine Sputum Culture

Medically reviewed by Debra Sullivan, PhD, MSN, RN, CNE, COI on January 5, 2016Written by Rachel Nall on July 25, 2012

What Is a Routine Sputum Culture?

When you have a respiratory tract infection or a lung-related disorder, your lungs produce a thick, substance known as sputum. This sputum can make it hard to breathe, cause coughing, and harbor bacteria. If you experience any of these symptoms, your doctor may ask for a sputum culture.

This fast, relatively painless test helps laboratory technicians study the bacteria or fungi that might be growing in your lungs and causing the production of the sputum. This can help them find the cause of your illness. The most difficult part of a sputum culture is often getting enough material in a sputum sample for testing.

What Uses Does the Test Have?

Sputum collects in the lower parts of your lungs and bronchi, which are the tube-like pathways that air moves through to reach your lungs. Symptoms that may indicate the need for a sputum culture test include:

  • cough
  • a fever or chills
  • fatigue
  • muscle aches
  • breathing difficulties
  • chest pain
  • confusion

The test can reveal what may be causing:

  • bronchitis
  • a lung abscess
  • pneumonia
  • tuberculosis
  • chronic obstructive pulmonary disease
  • cystic fibrosis

Certain harmful bacteria, viruses, or fungi can cause respiratory conditions. By determining what may be causing your symptoms, your doctor can find the best medication to cure the infection.

In some instances, your doctor may order a complete blood count to determine if white blood cells are elevated. This increase in white blood cells can indicate an infection.

How Is the Test Performed?

A sputum culture requires minimal effort on your part. You simply need to provide the sample for the lab to test. You’ll be asked to cough deeply to bring up the sputum from your lungs.

Saliva that can come up when someone is asked to cough is typically from the mouth and upper airways and isn’t useful for this test. A few techniques can be used to make the test most effective. Drinking plenty of fluids can help loosen the secretions and make it easier to cough up sputum. Your doctor may ask you to rinse out your mouth with clear water to help get rid of any other bacteria and extra saliva.

You’ll be asked to spit the sputum into a small cup. To cough deeply from your lungs, you might need to take three deep breaths before you cough forcefully. If any sputum comes up, you can spit it into the cup. The laboratory needs at least 2 milliliters of sputum for testing.

If you’re having trouble coughing up enough sputum, your doctor may try tapping on your chest to loosen the sputum. They may also have you inhale a steam-like mist to help you cough up the sample.

How Are the Results Interpreted?

Once you’ve produced a sputum sample for analyzing, the sample should be taken to the laboratory within one to two hours of coughing it up. The laboratory will take the sample and place it on a special plate that has a nutrient that helps bacteria or other pathogens present in your sputum grow.

The laboratory can run a number of tests to determine if the growth is a bacterium, a virus, or a fungus. Remember that some bacteria grow naturally in your airways without causing illness. The laboratory will work to tell the difference between bacteria that makes you sick and those that keep you well.

The laboratory will then give your doctor a report with the results.

What Are the Risks of the Test?

When you aren’t feeling well, the deep coughing associated with a sputum culture may feel uncomfortable. You may feel some chest discomfort after giving the sample.

However, there are no risks associated with having a sputum culture. If you’ve had abdominal surgery, your doctor may instruct you to hold a pillow over your stomach before coughing to minimize abdominal discomfort. This technique is known as splinting.

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