TB Culture

Does this test have other names?

Tuberculosis culture

What is this test?

This test finds out if you have tuberculosis (TB). TB a very contagious bacterial infection that is spread through the air. The test can be done on a sample of sputum. This is the mucus you cough up from your lungs. Or the test can be done on urine, cerebrospinal fluid (CSF), blood, or other tissue. The sample is put into a small dish with a substance that helps bacteria grow. This is known as a culture. After a period of time, the dish is checked to see what type of bacteria are growing. This test looks for bacteria called Mycobacterium tuberculosis.

Why do I need this test?

You may need this test if you had a positive screening test for TB. This may have been a skin test or blood test. A culture can find out if you have active TB or inactive (latent) TB. 

A TB culture can also help guide your treatment. Types of treatment vary. People with latent TB are not contagious. People with active TB are contagious and may spread the disease. If you have active TB, you may need months of treatment. This test is also done to check on TB treatment and see how it's working.

What other tests might I have along with this test?

Your healthcare provider may also order one or more of these tests:

  • Tuberculin skin test or a TB whole blood test. This is also called interferon gamma release assay. You may have one of these tests to find out if you have been exposed to TB. These tests are often done first. But they can't tell if you have active or latent TB. If the results are positive, you may have an acid-fast bacilli smear and a tuberculosis culture.

  • Acid-fast bacilli smear. This is a test done with your sputum. For this test, the sputum sample is stained with a special type of material to check for acid-fast bacteria.

  • Polymerase chain reaction test. This is a faster diagnostic test done most often on a sample of sputum.

  • Chest X-ray. This may be done to check your lungs. 

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

Tuberculosis culture results are negative if no Mycobacterium tuberculosis are found in the culture. Test results are positive if these bacteria are found in the culture. 

How is this test done?

If the infection may be in your lungs, your sputum will be tested. You will need to collect at least 3 samples on different days at least 8 to 24 hours apart. One of those samples should be an early morning sample. You may need to use an ultrasonic or nebulizing device to help bring up sputum.

If your healthcare provider thinks you have an infection elsewhere in the body, you may need to give a blood sample. In some cases, a tissue sample from the lungs is needed.

Specimens need to be collected in sterile containers and handled with care. Your samples will be placed in small dish with a substance that helps bacteria grow. Then a lab technician checks the samples under a microscope to see if the bacteria that cause tuberculosis have grown. 

The results of a tuberculosis culture can take many weeks. Rapid culture tests give results within 36 to 48 hours. Rapid tests are not available in all hospitals. Ask your healthcare provider how long your results will take.

Does this test pose any risks?

Sputum testing does not pose any known risks.

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

What might affect my test results?

Taking antituberculosis medicine could prevent TB bacteria from growing in the culture.

How do I get ready for this test?

You don't need to prepare for this test. Your healthcare provider will give you specific directions for collecting the samples. Be sure your provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use. 

Online Medical Reviewer: Amy Finke RN BSN
Online Medical Reviewer: Chad Haldeman-Englert MD
Online Medical Reviewer: Tara Novick BSN MSN
Date Last Reviewed: 9/1/2022
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