health

A skin test known as the Mantoux or PPD (purified protein derivative)
test is used to diagnose primary tuberculosis. For this test, a small amount
of testing fluid is injected with a fine needle just beneath the skin on the
lower part of the arm. Two to three days later, a healthcare professional
checks the arm to see if a bump has formed at the site of the injection.
If a bump wider than a certain size is present (for most people, 10 to 15
millimeters of a half inch), the patient most likely has been infected by
TB bacteria; this is known as a positive test. Doctors may order more
tests, such as a chest x-ray and a test of sputum that is coughed up, to see
if secondary (active) tuberculosis is present.