Nursing care
Pulmonary Tuberculosis Screening: the nurse's role, start to finish
Written and reviewed by Dana Whitfield, RN, MSN · 5 min read · Updated September 2026
Short answer
Pulmonary tuberculosis screening nursing begins with the Mantoux tuberculin skin test, placed intradermally and read by measuring induration, not redness, at 48 to 72 hours. The millimetre cut-off for a positive result changes with the patient's risk group. A positive skin test confirms exposure, not active disease, so a chest X-ray and further workup follow.
Indications and contraindications
TB screening is indicated for healthcare workers on routine surveillance, new immigrants from high-burden countries, close contacts of a confirmed case, incarcerated individuals, people who are immunocompromised or HIV-positive, and anyone with symptoms suggestive of active disease, a persistent cough beyond three weeks, night sweats, unexplained weight loss, or haemoptysis.
The Mantoux test is contraindicated in anyone with a documented severe reaction to a previous test and in people already diagnosed with active or prior TB disease, since the result adds nothing and risks a significant local reaction. Interferon-gamma release assays, blood tests such as QuantiFERON-TB Gold, are the preferred alternative for patients who have received BCG vaccination, since BCG can cause a false-positive Mantoux result that the blood test does not share.
Getting the patient ready
Confirm BCG vaccination history and any prior TB skin test results before proceeding, since a documented history of a positive Mantoux means repeat skin testing is not useful and an IGRA or chest imaging is the more appropriate next step. Ask about symptoms directly, cough duration, fever pattern, weight loss, and night sweats, because a symptomatic patient needs isolation precautions considered alongside, not instead of, the screening test.
Explain the two-step nature of the process to the patient clearly: a small intradermal injection today, followed by a mandatory return visit in 48 to 72 hours for reading. Stress that the appointment to read the result is not optional and that the test cannot be reliably read by the patient at home, since this is the single most common reason screening data is incomplete. Document the injection site, typically the volar surface of the forearm, so the same site can be located and read accurately at follow-up.
Technique and safety checks
Draw up 0.1 mL of purified protein derivative and administer it intradermally using a 27-gauge needle at a 5 to 15 degree angle, bevel up, into the volar surface of the forearm. A correctly placed injection raises a pale wheal of 6 to 10 mm immediately; if no wheal forms, the dose was likely given subcutaneously and the test should be repeated at a different site, documented, rather than read as-is.
Do not massage or cover the site, and instruct the patient to avoid scratching it or applying a plaster. The critical safety and accuracy check comes at the reading appointment: read the result at 48 to 72 hours by palpating and measuring the induration, the raised, hardened area, in millimetres across the widest diameter of the arm, not along it. Measure induration only. Redness or erythema without palpable induration is not measured and does not count toward the result, a distinction that catches many learners early on.
What can go wrong
A false positive most often comes from prior BCG vaccination or infection with a nontuberculous mycobacterium, which is why IGRA testing is preferred in a BCG-vaccinated population. A false negative can result from testing too early after exposure, before the immune response has developed, from anergy in a significantly immunocompromised patient, from improper subcutaneous rather than intradermal injection, or from reading the site outside the 48 to 72 hour window.
Reading too early misses the peak of the delayed hypersensitivity reaction, and reading too late, beyond 72 hours, can also under-read a true result as the reaction begins to fade. If the patient misses the reading appointment entirely, the test must be repeated rather than assumed positive or negative, and this should be explained to the patient plainly at the time of placement so a missed window does not become a missed diagnosis.
Ongoing care
A positive skin test confirms exposure and infection, latent or active, but does not by itself diagnose active disease. The next step is a chest X-ray and, if that is abnormal or the patient is symptomatic, sputum collection for acid-fast bacilli smear and culture, ideally three early-morning specimens on separate days.
A patient confirmed to have active pulmonary TB needs airborne precautions, a negative-pressure room and an N95 respirator for anyone entering, until proven noninfectious, alongside referral for directly observed therapy. A patient with latent TB infection, positive skin test, normal chest X-ray, no symptoms, is offered treatment to prevent progression to active disease and needs education on completing the full course even though they feel entirely well throughout it.
Common exam questions
Expect an item asking what is measured when reading a Mantoux test, and the correct answer is induration in millimetres, not the diameter of redness. A companion item often gives a specific patient scenario, a healthcare worker, a homeless individual, or someone who is HIV-positive, and asks which induration size counts as positive, testing your knowledge that the cut-off is 5 mm for high-risk or immunocompromised patients, 10 mm for those with other risk factors such as recent immigration or congregate living, and 15 mm for people with no known risk factors.
You may also see a timing item: a nurse reads a test at 24 hours or at 96 hours and the question asks what to do, and the correct response is to repeat the test, since a reading outside the 48 to 72 hour window is not valid. Finally, expect at least one item distinguishing a positive skin test from active disease, since NCLEX writers frequently test whether you understand that a positive Mantoux alone does not mean the patient is contagious or needs airborne isolation.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our respiratory practice questions are the closest set to what this page covers.
Common questions
What size of induration counts as a positive Mantoux test?
It depends on risk group: 5 mm or more is positive for immunocompromised patients, close contacts of active TB, or those with chest X-ray changes consistent with prior TB. 10 mm or more is positive for higher-risk groups such as recent immigrants, healthcare workers, or residents of congregate settings, and 15 mm or more is positive for people with no known risk factors.
Why is the test read at 48 to 72 hours and not sooner?
The Mantoux test relies on a delayed-type hypersensitivity reaction, which takes time to develop after the intradermal injection. Reading before 48 hours can miss the peak reaction and under-read a true positive, and reading after 72 hours can also miss the window as the induration begins to subside.
Does a positive TB skin test mean the patient has active tuberculosis?
No. It confirms the patient has been infected with TB at some point, but does not distinguish latent infection from active disease. A chest X-ray, and sputum testing if the X-ray is abnormal or the patient is symptomatic, is needed to make that distinction.
Why do BCG-vaccinated patients get a blood test instead of a skin test?
BCG vaccination can cause a false-positive Mantoux result because the vaccine itself triggers an immune response similar to natural infection. An interferon-gamma release assay, a blood test, does not cross-react with BCG and gives a more reliable result in vaccinated patients.