Mycobacterium tuberculosis culture (from respiratory specimen)

This test, commonly called a TB culture, checks a sample from your body—most often sputum—to determine whether Mycobacterium tuberculosis, the bacteria that cause tuberculosis (TB), is present. Unlike a rapid screening test, a culture actually grows the bacteria in a laboratory, which allows your doctor to confirm an active TB infection.

A TB culture involves collecting a sample from your respiratory tract (such as sputum, induced sputum, or bronchial washings) and growing it in a controlled environment to detect *Mycobacterium tuberculosis*. This process can take weeks or months to produce results, as the bacterium grows slowly.

Your doctor may order this test if you have symptoms of active tuberculosis, such as a cough lasting more than three weeks, unexplained weight loss, night sweats, fever, or coughing up blood. It is also used to investigate an abnormal chest X-ray or a positive TB skin or blood test, and to monitor how well treatment is working.

Your healthcare provider may order this test if you have symptoms like persistent cough, fever, weight loss, or chest pain, especially if you live in an area with higher TB rates or have risk factors like weakened immunity, recent travel to high-risk regions, or exposure to someone with TB.

For most people, the sample collected is sputum, the mucus coughed up from deep in the lungs. You will usually be asked to provide an early-morning specimen on two or three separate days. If you cannot cough up enough sputum on your own, a respiratory therapist may help obtain a sample using a mist you inhale. In some cases, urine, tissue, or other body fluids may be collected instead.

You’ll likely need to provide a sputum sample (from coughing into a sterile container) or another respiratory specimen. If you’re unable to produce sputum, your doctor may use a procedure like a bronchoscopy to collect samples directly from your airways.

A positive culture means TB bacteria grew from your sample, confirming active tuberculosis. A negative result means no bacteria grew during the full observation period, though TB cannot always be completely ruled out early on. If bacteria do grow, the laboratory typically performs drug-susceptibility testing to identify which antibiotics will be most effective, helping your doctor choose the right treatment plan for you.

Results are reported as either **positive** (growth of *Mycobacterium tuberculosis* detected) or **negative** (no growth observed). A positive result confirms active TB, while a negative result means the test did not detect the bacterium at that time. Repeat testing may be needed if initial results are inconclusive.