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Sputum Culture
Sputum is the liquid that comes from your respiratory tract when you cough. Learn about what happens if your doctor orders a sputum culture.

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Sputum Culture and Analysis

Sputum is the liquid substance that comes from your respiratory tract when you cough. In addition to mucus, sputum contains many materials that are not visible to the naked eye. It often consists of bacteria, cellular fragments, blood, and pus.

A sample of your sputum can give your physician useful information for screening or diagnosing bacterial infections in the respiratory system.

What Does the Test Diagnose?

A sputum culture and analysis is used to diagnose lower respiratory tract infections caused by bacteria or fungi. It can be used to identify causes of the following symptoms:

  • coughing
  • chills and/or fever
  • difficulty breathing
  • chest pain
  • fatigue
  • muscle aches
  • confusion

If disease-causing bacteria are found on your sputum culture, the culture can be used to diagnose and identify appropriate treatment for:

  • bronchitis
  • lung abscess
  • pneumonia
  • tuberculosis
  • complications of chronic obstructive pulmonary disease (COPD)
  • infections in cystic fibrosis patients

How to Prepare for the Test

Check with your physician to find out if you should temporarily discontinue taking any medication prior to giving a sputum sample. Antibiotics, anti-inflammatory drugs, and steroids can affect the results of a sputum culture.

You may be advised to drink plenty of water and other liquids the night before giving your sputum sample. This will make it easier to cough up a sample the next morning. Prior to the test, you will be asked to rinse out your mouth.

How Is the Sample Collected?

The collection of a sputum sample may be done in a physician’s office, laboratory testing site, or hospital. In some cases, you may be instructed to collect your own specimen at home. A sputum sample collected at home should be taken to a laboratory as quickly as possible to ensure that it remains fresh.

You will get the best results if you provide a sample first thing in the morning, before you have food or drink. This will provide a sample with the sputum from the deepest part of your chest.

Prior to providing the sample, you will be instructed to rinse out your mouth with water or saline. This clears out microorganisms from your mouth. You will be asked to breathe deeply and then deeply cough. As you cough up the sputum, you will deposit it into a sterile collection cup.

For best results, it is important to ensure that the sample you provide includes sputum, not just saliva. The saliva will contain the microorganisms found in your mouth, not necessarily those causing an infection in your lungs. Saliva is watery; sputum usually is yellow and thick. In cases of infection, the sputum may be green or flecked with blood.

If you are unable to produce a sample of sputum, a sample can be induced by your physician or lab technician. You may be asked to inhale sterile saline or a glycerin aerosol, which will help loosen the sputum deep in your lungs.

How Is the Test Done?

Your sample will be taken to a laboratory for sputum culture and analysis.

A Gram stain test will identify that the sample is adequate and contains enough bacterial cells to proceed. This test involves placing a portion of the sample on a slide. The slide is stained with red and purple dyes and examined with a microscope.

The test may also help identify the type of bacteria that may be present. By looking at the bacteria’s reaction to the dyes and other characteristics, a technician can identify the bacteria as either gram-positive or gram-negative.

If adequate, the sample will be placed in a special plate that encourages the growth of the bacteria or fungi. This is the sputum culture. A bacterial infection may require up to 48 hours to grow. It may take a week or more for fungi to reproduce.

Sputum analysis involves using chemical tests and microscopes to examine the different types of bacteria and fungi present. Part of this identification process involves classifying the bacteria as either normal or disease-causing organisms. The disease-causing organisms are then tested to determine what antibiotics will work best to treat them.

What Are the Benefits of the Test?

Providing a sample for a sputum culture and analysis is noninvasive and requires little time. However, it can provide valuable information to your physician in identifying and diagnosing the cause of a respiratory infection. The results can help your physician determine an appropriate antibiotic or other course of treatment. It also can help your physician determine if an ongoing treatment is effective.

For some individuals, a bacterial respiratory infection can cause serious consequences. If you are elderly, have a suppressed immune system, lung damage, or a lung condition such as COPD or cystic fibrosis, finding prompt, accurate treatment is critical.

What Are the Risks of the Test?

Having a sputum sample collected for culture and analysis by coughing is safe. If you have a respiratory infection, the coughing required to produce the sample might cause discomfort.

How Are the Results Interpreted?

Your physician will receive the results of the sputum culture and analysis. Results may be available within a few days. However, some types of fungi may take a week or longer to grow for analysis.

If your results are “negative” or normal, there was no evidence of disease-causing bacteria or fungi in your sputum sample.

However, if symptoms persist, it may indicate the presence of a viral infection or other microorganism that wasn’t adequately represented in the sputum sample. Some types of organisms can’t be grown and identified with sputum culture, so additional testing may be necessary.

If your results are “positive” or abnormal, your physician will use the information in the sputum analysis to choose the most effective course of antibiotic treatment and therapy for your lung infection.

Written by: Anna Giorgi
Edited by:
Medically Reviewed by:
Published: May 9, 2016
Published By: Healthline Networks, Inc.
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