A TB skin test — formally the Mantoux test or Purified Protein Derivative (PPD) — screens for tuberculosis exposure. A trained healthcare worker injects a small amount of purified TB protein just under the skin of your forearm. You return 48 to 72 hours later for a trained reader to measure the response.
The reader measures the induration (the raised, firm area), not the redness. A positive reaction means your immune system has been exposed to TB bacteria at some point and produced an immune response — but it does not necessarily mean you have active disease. A negative reaction means no induration developed.
The TB skin test is the long-standing standard. It is widely accepted by schools, nursing programs, healthcare employers, childcare programs, and many immigration applications. The cost at our Ashburn lab is $89, which covers both the injection visit and the return reading.
A two-visit requirement is the main downside. If you miss the 48-to-72-hour reading window, the test must be repeated. For clients whose return visit is hard to schedule — and for clients vaccinated with BCG (which can produce false-positive skin reactions) — we recommend the single-visit QuantiFERON-TB Gold blood test instead. Same $89 price.