The tuberculin skin test (TST) -- also commonly known as the PPD and performed in a doctor's office or health department -- is a reliable detector of TB in most people. It is used to detect TB in individuals at risk for new infection, such as health care workers or close contacts of infected individuals, and those at increased risk due to a weakened immune system. A small amount of liquid purified protein derivative (PPD) from the TB bacteria is injected just under the top layer of skin on your arm. After two to three days, a doctor or nurse will evaluate your arm to see if the test is positive. If it is, you will have a hard, red welt at the injection site. A positive result means you have been infected with TB, even if the infection is not active.
If your test is positive, your health care provider will do a thorough physical exam and order an X-ray of your lungs to reveal whether the disease is active. For patients in whom there is high suspicion for lung infection with TB, other tests will be ordered using samples of your saliva. If these samples come back positive, you have active pulmonary TB.
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Whether or not your TB is active, you should be regularly monitored by your doctor.
What Is the Treatment for Tuberculosis?
Treatment for TB depends on whether it is active or latent.
Latent TB Infection
If you're infected with TB but don't have the active disease, your doctor will go over your risk factors for developing active TB and will discuss treatment options. An antibiotic called isoniazid (INH) is often prescribed to help prevent the dormant infection from becoming active.
Your doctor will likely have you take a daily dose of INH for nine months and evaluate you regularly to ensure that you're tolerating the drug without major side effects, which include hepatitis (liver inflammation) and peripheral neuropathy (nerve damage). The risks of taking INH increase with age. In addition, your doctor may recommend vitamin B6 (pyridoxine) to prevent specific side effects of INH. An alternative therapy includes therapy with INH and rifapentine (Priftin) given weekly for three months and directly observed by your health care worker. This regimen can have interactions with other medications and have significant side effects as well.