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TB Culture

Does this test have other names?

Tuberculosis culture

What is this test?

This test finds out if you have tuberculosis (TB), a highly contagious bacterial infection spread through the air. The test can be done on a sample of sputum, the mucus you cough up from your lungs, or it can be done on urine, cerebrospinal fluid (CSF), blood, or tissue. This test is also done to monitor TB treatment.

Why do I need this test?

You may need this test if screening tests for TB (skin tests or blood tests) are positive. A culture test or other diagnostic test is needed to find out if you have active TB or inactive (latent) TB.

People with latent TB are not contagious. Treatment for latent TB depends on various things and your own case. People with active TB are contagious and may spread the disease. If you have active TB, you may need months of treatment.

What other tests might I have along with this test?

Your healthcare provider also might order:

  • Tuberculin skin test or a TB whole blood test to find out whether you have been exposed to TB. These tests are typically done first. But they cannot tell whether 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 of your sputum. In this test, the sputum sample is stained with a special type of material to check for acid-fast bacteria.

  • Polymerase chain reaction test, a newer, faster diagnostic test done on a sample of sputum.

  • Chest X-ray to view the lungs

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Tuberculosis culture results are negative if no acid-fast bacilli grow in the culture. Test results are positive if these bacteria grow. 

How is this test done?

If healthcare providers suspect the infection is in your lungs, your sputum will be tested. You will need to collect 3 to 5 samples on different days, most likely in the early morning. You may need to use an ultrasonic or nebulizing device to help bring up sputum.

If healthcare providers suspect the infection is in your kidneys, your urine will be tested. You'll need to collect 3 to 5 single samples of urine taken early in the morning.

If your provider suspects you have an infection elsewhere in the body, you may have to give a blood sample. In a few 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 special dish with a substance that promotes bacterial growth. This is a culture. Then a lab technician checks the samples under a microscope to see if the bacteria that cause tuberculosis, Mycobacterium tuberculosis (or acid-fast bacilli), have grown. 

Until recently, the results of tuberculosis cultures could take many weeks. Newer, more rapid culture tests give results within 36 to 48 hours.

Does this test pose any risks?

Sputum and urine testing do not pose any known risks.

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Taking anti-tuberculosis medicine could prevent TB bacteria from growing on the culture medium.

How do I get ready for this test?

You don't need to prepare for this test. Your healthcare provider will give you specific instructions 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 illicit drugs you may use. 

Medical Reviewers:

  • Hanrahan, John, MD
  • Sather, Rita, RN