Making a diagnosis of tuberculosis typically includes a review of the patient's medical history, a physical exam, and a TB skin test. However, a positive TB skin test doesn't necessarily mean the person has active tuberculosis. There are other tests, such as x-rays and sputum samples, that can be administered after a positive TB skin test result to confirm whether theperson has active tuberculosis. Because tuberculosis bacteria grow very slowly, it can take up to 4 weeks to confirm the diagnosis.
An Overview of Tuberculosis Diagnosis
Tuberculosis may be suspected based on the patient's medical history (including current symptoms and medical conditions) and a physical exam.
Specific tests will help the doctor make the tuberculosis diagnosis and determinewhether it is active or latent tuberculosis (see Latent Versus Active Tuberculosis). These tests can include a TB skin test (PPD test) and other tests, such as a chest x-ray and samples of sputum.
TB Skin Test for Diagnosing Tuberculosis
A tuberculosis (TB) test can be effective in determining whether a person has been infected with the tuberculosis bacteria. There are two types of this test: theskin test and the blood test. To identify those who may have been exposed to tuberculosis, healthcare providers typically inject a substance called tuberculin under the skin of the forearm. If a red welt forms around the injection site within 72 hours, the person may have been infected. This doesn't necessarily mean he or she has active tuberculosis. People who may test positive on the tuberculintest include:
Most people with previous exposure to tuberculosis bacteria (Mycobacterium tuberculosis)
Some people exposed to bacteria related to the TB bacteria
Some people born outside the United States, who were vaccinated with the TB vaccine used in other countries.
Other Tests Used to Make a Diagnosis
If people have a positive TB test, other tests can help to show if they have activetuberculosis. In making a diagnosis of active tuberculosis, doctors rely on symptoms and other physical signs, the person's history of exposure to tuberculosis, and x-rays that may show evidence of a tuberculosis infection.
The healthcare provider will also take sputum and other samples to see if the TB bacteria will grow in the lab. If bacteria are growing, this positive culture confirms atuberculosis diagnosis. Because M. tuberculosis grows very slowly, it can take up to 4 weeks to confirm the diagnosis. An additional 2 to 3 weeks are usually needed to determine which antibiotics to use to treat the disease.
An Overview of the TB Test
There are two types of TB (tuberculosis) tests. One is a TB skin test (also known as a PPD test) and the other is a TB blood test(QuantiFERON®-TB Gold).
What Is the TB Skin Test?
A tuberculosis skin test is a TB test that is often used to detect latent tuberculosis. You can get a skin test at the health department or at your doctor's office. A healthcare worker will inject a small amount of testing fluid (called tuberculin or PPD) just under the skin on the underside of the forearm. After 2 or 3 days, you must return to haveyour skin test read by the healthcare worker. You may have a swelling where the tuberculin was injected. The healthcare worker will measure this swelling and tell you if your reaction to the tuberculosis skin test is positive or negative. A positive reaction usually means that you have been infected by someone with active tuberculosis.
If you have recently spent time with and been exposed tosomeone with active TB, your TB skin test reaction may not be positive yet. You may need a second skin test 8 to 10 weeks after the last time you spent time with the person. This is because it can take several weeks after infection for your immune system to react to the TB skin test. If your reaction to the second test is negative, you probably do not have latent TB infection.
Blood Test for TB...