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Introduction ⬇

The intradermal tuberculin skin test detects TB infection; it does not distinguish active TB from dormant TB. PPD tuberculin is a protein fraction of the tubercle bacilli; when it is introduced into the skin of a person with active or dormant TB infection, it causes a localized skin erythema and induration at the injection site because of accumulated small, sensitized lymphocytes.

The Mantoux test is the TB skin test of choice. The tuberculin is injected into the intradermal skin layer with a syringe and fine-gauge needle. The multiple puncture test (tine test) is used for screening purposes for persons without symptoms, but the Mantoux test is far more accurate.

The two-step TB skin test is done to reduce the likelihood that a “boosted” reaction will be interpreted as a recent infection. The two-step skin test is not routine for contact case investigation.

  1. Persons who exhibit signs (x-ray film abnormality) or symptoms (e.g., cough, hemoptysis, weight loss) suggestive of TB.

  2. Recent close contacts with persons known to have or suspected of having TB.

  3. Persons who show abnormal chest x-rays compatible with past TB exposure.

  4. Members of groups at high risk for M. tuberculosis infection, such as immigrants from countries where TB is common (Africa, Asia, the Caribbean, Eastern Europe, Latin America, and Russia) or those who live or work in long-term care settings, correctional institutions, or homeless shelters.

  5. The two-step test is indicated for individuals who will be subject to periodic retesting (such as employees or residents of long-term care facilities). Using the two-step test reduces the change that a subsequent skin test will result in a boosted reaction that could be misinterpreted as a recent TB infection.

  1. The test should be read 48–72 hours after injection.

  2. Examine the injection site in good light.

  3. The patient should flex the forearm at the elbow.

  4. Inspect the skin for induration (hardening or thickening).

  5. Rub finger lightly from the normal skin area to the indurated zone (if present).

  6. Circle the zone of induration with a pencil and measure the diameter in millimeters perpendicularly to the long axis of the forearm. Disregard erythema if it occurs without induration; it is clinically insignificant.

  7. Large reactions may still be evident 7 days after the test.

Clinical Alert

  1. Tuberculin test material should never be transferred from one container to another.

  2. Intradermal skin tests should be given immediately after the tuberculin is drawn up.

  3. The greatest value of tuberculin skin testing (TST) is in the negative results; a negative test result in the presence of signs and symptoms of lung infection is strong evidence against active TB in most cases.

  4. A presumptive diagnosis of TB must be bacteriologically confirmed.

  5. In the United States, the incidence of TB is highest among foreign-born persons. The rate of TB has steadily declined in the United States since a peak in 1992.

  6. TB is acquired through close, frequent, and prolonged exposure to infected persons.

  7. Persons who have received BCG vaccine prophylactically or for bladder cancer treatment have a false-positive result on a TB skin test. Reactions of 5–10 mm may be caused by BCG vaccination. However, unless the vaccination was very recent, tuberculin reactions more than 10 mm should not be attributed to BCG.

  8. Periodic chest x-ray films are valuable adjuncts for monitoring patients who test positive because there is no sure way of predicting who will develop active TB.

  9. BCG is a freeze-dried preparation of a live, attenuated bovine strain of mycobacteria. It is used for TB immunization in children (e.g., infant with a negative TB test who lives in a household with untreated or ineffectively treated cases of TB) in countries with a high incidence of TB.

  10. Healthcare providers in contact with suspected or confirmed TB must wear a properly fitted, high-efficiency, dust- and mist-proof mask.

  1. The test interpretation is based on the presence or absence of induration.

  2. Negative or insignificant reaction: zone of induration less than 5 mm in diameter, unless the patient has HIV, organ transplant, or recent close contact with a person who has TB; positive or significant reaction: zone of induration more than 10 mm in diameter in persons at high risk.

  3. For persons in good health with no risk factors, an induration of 15–20 mm usually is considered positive. However, because those who are at increased risk for TB (in poor health) have decreased hypersensitivity, a 5-mm induration may be considered positive. Retest within 3 weeks. See Chart 7.2 for classification of test results.

Reactions can be categorized according to the following factors:

  1. Factors related to person being tested:

    1. Viral infections (measles, mumps, chickenpox)

    2. Live virus vaccinations (measles, mumps, polio)

    3. Nutritional factors (severe protein depletion)

    4. Diseases affecting lymphoid organs (Hodgkin disease, lymphoma, chronic lymphocytic leukemia, sarcoidosis)

    5. Drugs (corticosteroids, other immunosuppressive agents)

    6. Age (newborns, older patients with waned sensitivity)

    7. Recent or overwhelming M. tuberculosis infection

  2. Factors related to tuberculin injected:

    1. Improper storage (exposure to light, heat)

    2. Improper dilution

    3. Chemical denaturation

    4. Contamination

    5. Absorption (partially controlled by adding Tween-80)

    6. Outdated material

  3. Factors related to method of administration:

    1. Injection of too little or too much antigen

    2. Delayed administration after drawing up dose

    3. Injection too deep or too shallow

  4. Factors related to test interpretation and recording of results:

    1. Test not read within prescribed time frame

    2. Inexperienced or improperly trained reader

    3. Conscious or unconscious bias

    4. Recording error

    5. Measurement error

Procedure ⬆ ⬇

Procedure for Intradermal Skin Test (Mantoux)

  1. Observe standard precautions.

  2. Draw up PPD tuberculin into a tuberculin syringe (follow manufacturer’s directions carefully). Use 0.1 mL for each test.

  3. Cleanse the skin on the volar or dorsal aspect of the forearm with alcohol and allow it to dry.

  4. Stretch the skin taut.

  5. Hold the tuberculin syringe close to the skin so that the hub of the needle touches the skin as the needle is introduced, bevel side facing up, under the skin. A discrete, pale elevation of the skin (wheal) 6–10 mm in diameter should be produced when the prescribed amount of PPD tuberculin is injected into the intradermal skin layer.

  6. For the two-step test, administer the Mantoux intradermal skin test, as described, for all persons for whom testing is indicated. Strictly enforce reading of results in 48–72 hours. If the result is positive, do not administer a second PPD dose but refer the patient for follow-up. If induration is present but does not classify as positive, retest immediately on the patient’s other arm and read the results in 48–72 hours. If the result of the first Mantoux test is negative, retest in 1–2 weeks, using the same PPD dose and the same arm as for the first test. Read the results in 48–72 hours. If the reaction at second test is negative (no induration), perform no further testing. Make plans to administer the one-step Mantoux test annually.

  7. Document site of test for follow-up reading of results.

Clinical Implications ⬆ ⬇

  1. The test should be read 48–72 hours after injection. The larger the area of the skin reaction, the more likely it is to represent TB infection. An indurated area of 5 mm or more is positive in people with HIV, with organ transplants, or with recent close contact with a person who has TB. An indurated area of 10 mm or more is positive in recent immigrants, intravenous drug users, employees and residents of high-risk settings, children younger than 4 years, and others in high-risk categories. An induration of 15 mm or more is positive in any other person. False-positive reactions can occur from previous bacille Calmette-Guérin (BCG) vaccination, or problems with administration of or reading the skin test.

  2. A significant reaction does not distinguish between active and dormant TB infection; the stage of infection can be determined from the results of clinical bacteriologic sputum tests and chest roentgenograms.

  3. A significant reaction in a clinically ill patient means that active TB should be considered as a cause for illness. With HIV infection, a reaction of 5 mm or more is considered positive.

  4. A significant reaction in a healthy person usually signifies either healed TB or an infection caused by a different mycobacterium. Chest x-rays can confirm the absence of an active infectious process.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of and procedure for TB skin test; convey the importance and necessity of returning for reading of the skin reaction. Obtain history of occupation, living conditions, and reason for testing.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results within the prescribed time; report and record findings. Modify the nursing care plan as needed. Monitor and counsel the patient appropriately about the need for chest x-ray and sputum cultures for those with positive TB skin tests. Discuss initial and continued therapy and institute infection and case control as required. The possibility of TB infection must be ruled out before preventive therapy can start. TB is a reportable infection to local, state, and federal authorities.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆ ⬇

False-negative results may occur even in the presence of active TB or whenever sensitized T lymphocytes are temporarily depleted in the body.

Reference Values ⬆

Normal

Reaction negative or not significant