Tb Screening Updates: New Diagnostics and Why Testing Protocol Is Changing
Q1: What does a positive TB skin test look like on dark skin?
A1: The test presents with the same structural characteristic: a distinct, elevated, firm swelling beneath the skin surface. While light skin may show visible erythema, dark skin often shows no surface redness at all, or it may exhibit a subtle localized hyperpigmentation. Clinicians rely strictly on physical palpation with their fingers to outline and measure the induration borders, ensuring visual skin tone differences do not distort the reading.
Q2: Can I scratch or cover the injection site if it itches?
A2: Do not scratch, bandage, or apply hydrocortisone creams to the test area. Mechanical irritation from scratching can trigger localized swelling, artificially enlarging the induration and causing an inaccurate measurement. If the area itches, apply a cool, damp washcloth for several minutes without applying direct pressure or rubbing the site.
Q3: How soon after exposure will a skin test show a positive bump?
A3: The immune system takes between 2 and 8 weeks to mount a detectable T-cell memory response following exposure to *Mycobacterium tuberculosis*. Testing too early can generate a false-negative reading. If an individual experiences a known exposure, physicians often perform a baseline test immediately, followed by a repeat test 8 to 10 weeks later to detect potential seroconversion.
