Routine Sputum Culture

Written by Rachel Nall | Published on July 25, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP

What is a Routine Sputum Culture?

When you develop a respiratory tract infection or experience a lung-related disorder, a thick, mucus-like substance known as sputum is produced in the lungs. 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 causing the production of the sputum and therefore to pinpointing 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 on the lower parts of your lungs and bronchi, which are tube-like pathways that air moves through to reach your lungs. Symptoms, such as the following, may indicate the need for a sputum culture test:

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

The test can reveal the pathogen that may be causing one of the following conditions:

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

A number of harmful “bugs” (bacteria, viruses, or a fungi) can cause respiratory conditions. By pinpointing what may be causing your symptoms, your doctor can determine the best medication to cure the infection.

In some instances, your doctor may order a complete blood count (CBC) along with the test 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 will be asked to cough deeply to bring up the mucus-like sputum from your lungs. Saliva that can often comes up when someone is asked to cough is typically from the mouth and upper airways and is not 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, making sputum easier to cough up. Your doctor may ask you to rinse out your mouth with clear water to help get any other bacteria and extra saliva..

You will be given a small cup to spit the sputum into. To really cough deeply from your lungs, you might 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 mL of sputum for testing.

If you’re having trouble producing this much sputum, your provider may try tapping on your chest to loosen the sputum. He or she may also have you inhale a steam-like mist to help you cough up the sample.

How Are the Results Interpreted?

Once you have 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.

Your doctor will then be given a report with the results.

What Are the Test’s Side Effects?

When you aren’t feeling well, the deep coughing associated with a sputum culture may feel uncomfortable. You may feel some chest discomfort after taking the sample. However, there are no risks associated with obtaining a sputum culture. If you have undergone abdominal surgery, your provider 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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