How It Works
Walk In
15-Minute Visit
Return for PPD Reading in 24-48 Hours
What is a TB Skin Test?
The TB skin test (also called the PPD test or Mantoux test) detects whether you've been exposed to tuberculosis bacteria at some point in your life. It works by injecting a small amount of purified protein derivative (PPD) — a harmless extract of TB proteins—just under the skin of your forearm.
If your immune system has seen TB bacteria before, your body will produce a small raised reaction at the injection site within 48 to 72 hours. A trained technician measures the size of that reaction to determine whether the test is positive or negative.
How the PPD Test Works
The TB skin test is called the Mantoux method — the standard for intradermal TB testing.
Here's what happens during your test:
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Placement (Day 1): A trained technician injects 0.1 mL of PPD tuberculin solution just under the top layer of skin on your inner forearm. A small bubble (called a wheal) appears at the injection site. This is normal.
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Waiting Period (48-72 hours): Your immune system has 48 to 72 hours to react. If you've been exposed to TB before, your body recruits immune cells to the injection site, creating a raised, firm bump (called induration). Don't scratch, cover, or apply anything to the injection site during this time.
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Reading (Day 3): A trained technician measures the induration — not the redness, but the firm, raised area.
The size of the induration determines whether the test is positive based on CDC guidelines.
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The PPD skin test is recommended by the CDC for TB screening in most healthy adults. It is accepted by U.S. healthcare employers, schools, immigration authorities, and most occupational health programs.
TB Skin Test FAQ
Do I need an appointment for a TB skin test? No. We're a walk-in lab — no appointment, no doctor's order, no insurance card required. Walk in Monday through Friday, 7 AM to 5 PM for your placement, and return 48-72 hours later for the reading. Most placements take about 15 minutes from check-in.
What happens if I miss the 48-72 hour reading window? If you can't make it back within 72 hours, the test is no good — the reaction on your arm keeps changing past that point and can give a false read. You'd have to come back, get a new placement, and wait another 2-3 days. So if your timeline is tight, plan your placement on a day you can definitely return — or skip the skin test and go with the QuantiFERON Gold blood test instead. One visit, no return trip, results in 24-48 hours.
Do you take insurance for the TB skin test? No — we don't bill insurance for any of our walk-in tests, including the TB skin test (PPD). That keeps the price simple and the visit fast. Our price covers both visits (placement and reading) with no surprise bills, no insurance hold-ups, and no co-pay paperwork.