TB Manual

A.1. Tuberculin skin test (TST) administration and interpretation

A.1.1. Administration of TST

The only internationally recommended method of tuberculin skin testing is the Mantoux technique, which consists of intradermal injection of tuberculin material on the inner surface of the forearm. The instructions on how to perform this technique have been reproduced and adapted,7,17 with supporting videos available.18

A.1.1.1. Handling the solution

  • The purified protein derivative (PPD) should be stored between 2° and 8 °C and never frozen. Discard the solution if it freezes.

  • Remove the tuberculin solution from the vial under aseptic conditions. A little more than 0.1 mL of PPD solution should be drawn into the TB syringe. Hold the syringe upright and lightly tap out the air, then expel one drop. Check that a full 0.1 mL remains in the syringe.

  • Do not transfer the solution from one container to another, as the potency of the PPD may be diminished.

  • Draw up the solution just before injecting it. Do not preload syringes for later use as the potency of the PPD may be diminished.

  • The solution can be adversely affected by exposure to light. PPD should be stored in the dark except when doses are actually being withdrawn from the vial.

  • Use the solution within one month after opening, as the potency of the solution may be diminished. Label each bottle with the discard date when it is opened.

A.1.1.2. Preparing the person to be tested

  • Seat the person comfortably and explain the procedure.

  • Use the inner aspect of the forearm, preferably the nondominant arm (where administration and reading of the reaction is easiest), about 10 cm (4 inches) below the elbow; avoid areas with abrasions, swelling, visible veins or lesions. If there is a localized rash, a burn or localized eczema, avoid this area.

  • If neither forearm is suitable, use the outside of the forearm or the upper arm. In this case mark the location clearly in the record.

  • Cleanse the area to be injected with an alcohol swab and let the area dry.

  • Do not use EMLA® cream (or similar local anesthetic cream), as application of this cream has been reported to cause localized edema, which could easily be confused with a positive TST result.

A.1.1.3. Injecting the PPD tuberculin solution

  • Use a 0.6 to 1.3 cm (¼ to ½ inch), 26- or 27-gauge needle with a disposable plastic tuberculin syringe.

  • Position the bevel of the needle so that it opens facing up.

  • While holding the skin of the inner aspect of the forearm taut, insert the needle at a 5°-15° angle to the skin without aspirating. The tip of the needle will be visible just below the surface of the skin. The needle is inserted until the entire bevel is covered (see Appendix Figure A1).

    Figure A1. Technique of TST administration.

  • Administer the PPD by the slow intradermal injection of 0.1 mL (5 tuberculin units).

  • A discrete, pale elevation of the skin (a wheal) 6-10 mm in diameter should appear. The wheal will typically disappear in 10-15 minutes. The size of the wheal is not completely reliable, but if a lot of liquid runs out at the time of injection and there is no wheal, then repeat the injection on the opposite forearm, or on the same forearm as before, but at least 5 cm from the previous injection site.

  • A drop of blood may be seen — this is normal. The person tested should be offered gauze to remove the blood but should be advised not to massage the site in order to avoid squeezing out the PPD and disrupting the test.

  • Do not cover the site with a bandage.

  • Tell the patient that they should not scratch the site but may perform all normal activities, including showering or bathing.

  • Place uncapped disposable needles and syringes in appropriate puncture-resistant containers immediately after use.

  • If the TST is accidentally given as a subcutaneous or an intramuscular injection, this should not pose a serious risk of harm. It is possible that tuberculin-sensitive persons may have localized inflammation, which should be self-limited. It would not be possible to take a measurement of, or clinically interpret, any such reaction, so the TST should be administered again immediately using proper intradermal technique on the volar surface of the forearm.

  • After administration, record the following:

    • Date of injection

    • Dose of PPD (5 tuberculin units, 0.1 mL)

    • PPD manufacturer

    • PPD lot number

    • Expiration date of the PPD reagent

    • Site of injection

    • Person administering the TST.

  • In settings where TST administration may be unsupervised or performed by persons with minimal experience, the quality of TST administration may be assessed by following mobile TST (mTST) protocols,17,18 whereby photos of the wheal created after administration are taken and evaluated by an experienced reviewer.

A.1.2. Precautions

  • Acute allergic reactions, including anaphylaxis, angioedema, urticaria and/or dyspnea, have been rarely reported as temporally (not necessarily causally) associated with administration of Tubersol®.108 The events have been reported in Canada at a rate of less than 1 per million doses; some were reported in persons without a prior history of TST.

  • Epinephrine hydrochloride solution (1:1000) and other appropriate agents should be routinely available for immediate use in case an anaphylactic or other acute hypersensitivity reaction occurs. Health care providers should be familiar with the current recommendations of the National Advisory Committee on Immunization for monitoring of the patient for immediate reactions over a period of at least 15 minutes after inoculation and with the initial management of anaphylaxis in non-hospital settings.

The following persons can receive a TST:

  • Those with a history of receiving BCG vaccination(s).

  • Those with a common cold.

  • Those who are pregnant or are breast-feeding.

  • Those immunized within the previous four weeks with vaccines other than those listed below (live-virus vaccines).

  • Those with a previous positive TST.

  • Those taking low doses of systemic corticosteroids. A steroid dose equivalent to ≥15 mg prednisone daily for 2-4 weeks is required to suppress tuberculin reactivity.109,110

The following persons should NOT receive a TST:

  • Those with positive, severe blistering TST reactions in the past or with extensive burns or eczema present over TST testing sites, because of the greater likelihood of adverse or severe reactions.

  • Those with documented TB disease or a well-documented history of adequate treatment for TB infection or disease in the past. In such patients, the test is of no clinical utility.

  • Those with current major viral infections (eg, measles, mumps, varicella).

  • Those who have received live virus immunization within the past 4 weeks, as this has been shown to increase the likelihood of false-negative TST results.111 Note that only measles vaccination has been shown to cause false-negative TST results, but it would seem prudent to follow the same 4-week guideline for other live-virus immunizations, including mumps, rubella, varicella (chickenpox) and yellow fever. However, if the opportunity to perform the TST might be missed, the TST should not be delayed for live-virus vaccines since these are theoretical considerations.

    • Note: A TST may be administered before or on the same day as the immunizations but at a different site.

A.1.3. Measuring induration

  • The TST should be read by a trained health professional. Individuals without experience in reading a TST may not feel slight induration, and the TST would be mistakenly recorded as 0 mm.

  • Self-reading is very inaccurate and is strongly discouraged.112

  • Reading should be performed 48 to 72 hours after administration, as maximum induration can take up to 48 hours to develop, but after 72 hours it is difficult to interpret a reaction. Reactions may persist for up to one week, but for as many as 21% of individuals with a positive reaction at 48 to 72 hours, the reaction will be negative after 1 week.113 If the TST cannot be read within 72 hours, it should be repeated at a location far enough from the previous test that the reactions do not overlap. There is no minimum wait time and the test can be readministered immediately.

  • The forearm should be supported on a firm surface and slightly flexed at the elbow. Induration is not always visible. Palpate with fingertips to check if induration is present. If there is induration, mark the border of induration by moving the tip of a pen at a 45° angle laterally toward the site of the injection (Appendix Figure A2). The tip will stop at the edge of the induration, if present. Repeat the process on the opposite side of the induration. This pen method has advantages of being as reliable as the traditional palpation method (which relies entirely on fingertips) among experienced readers, and of being easier for new readers to learn and use.7

  • Using a caliper, measure the distance between the pen marks, which reflects the diameter of the induration at its widest transverse diameter (at a right angle to the long axis of the forearm). A caliper is recommended because readings will be more precise and setting the caliper may reduce rounding error. If a caliper cannot be found a flexible ruler could be used.

  • Do not record erythema (redness). Approximately 2-3% of persons tested will have localized redness or rash (without induration) that occurs within the first 12 hours. These minor allergic reactions do not indicate TB infection and they are not a contraindication to future TSTs.114

  • Blistering, which can occur in 3 to 4% of subjects with positive tests, should be recorded.

  • Record the result in millimeters (mm). Record no induration as “0 mm.” Recordings of positive, negative, doubtful, significant and non-significant are not recommended.

  • Do not round off the diameter of the induration to the nearest 5 mm, as this can interfere with determining whether TST conversion has occurred in the event of a future TST. If the measurement falls between demarcations on the ruler, the smaller of the two numbers should be recorded.

  • After measuring, record the following and provide a record of the result to the patient:

    • Date the induration was read

    • Measurement of the induration, if any, in mm

    • Any adverse reactions (eg, blistering)

    • Name of the individual reading the test

  • In settings where TST measurement may be unsupervised or performed by persons with minimal experience, the quality of TST measurement may be assessed by following mTST protocols,17,18 whereby photos of the induration are taken and evaluated by an experienced reviewer. This method is most accurate when applied to no or large indurations. In all settings, routine quality control and quality assessment measures of TST induration measurement should be employed to maximize accuracy.

    Figure A2. Ballpoint pen method for measuring the transverse diameter of the TST induration.

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Appendix 1
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A.2. Reproducibility and causes of TST and IGRA variation