TUBERCULIN PPD RT 23 AJV

INJECTION

**2.2 Dosage and administration** **Dosage and strength** The dosage is always 0.1 mL regardless of the strength used. Tuberculin PPD RT 23 AJV is injected intradermally. The strength 2 T.U./0.1 mL is recommended. **Injection technique** - 0.1 mL is administered with a 1 mL graduated syringe fitted with a short bevel needle (gauge 25 or 26). - The injection must be given strictly intradermally on the flexor surface of the forearm at the junction of the upper third with the lower two‐thirds. Administration near the wrist or the elbow joint may weaken the reaction. - The skin is slightly stretched, and the needle is held almost parallel with the skin surface, with the bevel upwards. The tip of the needle is inserted into the superficial layer of the dermis. - The needle should be visible through the epidermis during insertion. The 0.1 mL is slowly injected and a small blanched papule of 8–10 mm in diameter appears. This papule will disappear after approximately 10 minutes. - If no papule appears, the injection has been given too deep, and the skin test should be repeated on the other arm or on the same arm, at least 4 cm away from the first injection site. National recommendations regarding the administration of the Mantoux tuberculin skin test may be taken into consideration. **Evaluating the reaction** A skin test reaction is seen as a flat, uneven, slightly raised induration surrounded by an area of redness. The induration should be evaluated 48–72 hours after the injection. After approximately 72 hours, the size of the induration is expected to diminish. Only the induration is assessed. The diameter of the induration is measured in millimetres transversely to the long axis of the forearm with a transparent, flexible plastic ruler. Recommendations for interpreting the Mantoux tuberculin skin test are shown in Table 1.  Alternative interpretations, depending on national recommendations, individual and epidemiological factors, may be applied. **Interpretation** A positive reaction indicates an immune response for one or more of the following reasons: - Infection with _Mycobacterium tuberculosis_ complex, including _M. tuberculosis_, _M. bovis_, _M. africanum_, _M. microtii_ or _M. tuberculosis_ subsp. _caprae_. - Infection with non-tuberculous mycobacteria. - Previous BCG vaccination. BCG-vaccinated individuals normally become tuberculin-positive after 4–8 weeks. Reactions larger than 15 mm are unlikely to be due to previous BCG vaccination or exposure to environmental mycobacteria. **Waning of tuberculin sensitivity** In most individuals, tuberculin sensitivity caused by infection with _M. tuberculosis_ or related mycobacteria normally persists throughout life, but may decrease or disappear gradually in some individuals. The tuberculin sensitivity frequently wanes within a few years in BCG-vaccinated individuals. **Booster effect** If tuberculin is administered to individuals whose tuberculin sensitivity has waned, the reaction to the skin test will be weak or absent. Retesting with tuberculin weeks or months later may result in an accentuation of the response, i.e. a booster effect. Repeated tuberculin skin testing will not induce a positive reaction in individuals who have no previous cellular immunity against the antigens in tuberculin PPD. **Repeated tuberculin skin testing** If the tuberculin skin test is likely to be repeated, e.g. in health care workers potentially exposed to tuberculosis infection, a two-step method is recommended. Individuals with a weak or an absent initial Mantoux tuberculin skin test should undergo a second tuberculin skin test 2–4 weeks after the first test. Skin test conversion in such individuals is defined as a reaction to the second test of more than 10 mm and an increase of at least 6 mm compared to the first test. Individuals with skin test conversion after the second test should be considered to be previously infected with mycobacteria or may have been BCG vaccinated, whereas those with a negative reaction to the second test should be considered uninfected. It is important to emphasise that the predictive value of the skin test result and the expected risk of tuberculosis should be considered on an individual basis.