TB Screening on the NCLEX
PPD reading rules by risk group, IGRA, latent vs active, N95 and negative pressure.
TB screening is pure rules, and NCLEX tests every one of them. Learn the three induration cutoffs cold.
PPD (Mantoux) mechanics
0.1 mL intradermal, forearm, creates a wheal. Read at 48 to 72 hours. Measure induration (the firm raised area), never redness. Measure across the forearm's width. A patient who cannot return in 72 hours needs a new test or an IGRA.
Positive cutoffs by risk
≥5 mm: HIV, immunosuppressed (organ transplant, prolonged steroids), recent close contact of active TB, chest x-ray evidence of old TB. ≥10 mm: recent arrivals from high-prevalence countries, IV drug users, healthcare workers, residents and staff of congregate settings (prisons, shelters, long-term care), children under 4, other high-risk medical conditions. ≥15 mm: everyone else, no risk factors. The sicker or more exposed the patient, the smaller the induration that counts.
IGRA (blood test)
Interferon-gamma release assay (QuantiFERON, T-SPOT). One visit, no return trip, no reader subjectivity, and not confounded by prior BCG vaccination, so it is preferred for BCG-vaccinated patients and unreliable returners. Like the PPD, it cannot distinguish latent from active TB.
Latent vs active
Latent: positive screen, no symptoms, normal chest x-ray, not infectious. Treated (for example with rifampin or isoniazid regimens) to prevent activation. Active: cough over 3 weeks, hemoptysis, night sweats, fever, weight loss. Workup: chest x-ray, then sputum for AFB smear and culture (early morning specimens). Active disease is infectious and reportable to public health. A positive PPD alone never equals active TB; the follow-up chest x-ray is the tested next step.
Isolation rules
Suspected or confirmed active pulmonary TB: airborne precautions, negative-pressure room, door closed, N95 (fit-tested) for staff. The patient wears a plain surgical mask during transport, not an N95. Release from isolation generally requires effective therapy, clinical improvement, and consecutive negative AFB smears per policy.
One more classic
A prior positive PPD stays positive for life. Never repeat the PPD on a known converter: screen with symptom review and chest x-ray instead.
Frequently asked
Induration 11 mm in a nursing student?
Positive. Healthcare workers use the 10 mm cutoff. Next step: chest x-ray and symptom screen.
BCG-vaccinated patient needs screening?
Use an IGRA. BCG can cause false-positive PPDs but does not affect IGRA results.
Redness 20 mm, induration 0 mm?
Negative. Only induration counts.
Quick check
Loading a question…
How ready are you right now?
10 real NCLEX questions, free, in your browser. See how close you are to ready and which subjects are costing you.
Try 10 questions free