Page 202 - fourth year book

COMMUNICABLE DISEASES (T.B)

Contraindication:

o Known TB infection.
o Previous severe reaction to previous TST (e.g., necrosis, blistering,
anaphylactic shock, or ulcerations)
o Presence of skin rash that would make it hard to read the skin test.

o Inability of the case to return visit for reading the result

Procedure:

- It also called the Mantoux tuberculin skin test. It is performed by
injecting 0.1 ml of tuberculin purified protein derivative (PPD) into

the inner surface of the forearm. The injection should be made with a
tuberculin syringe, with the needle bevel facing upward. The TST is
an intradermal injection.

- When placed correctly, the injection should produce a pale elevation
of the skin (a wheal) 6 to 10 mm in diameter. The health care worker
must measure only the Induration (hard, dense, raised formation)
using a ruler. Redness by itself is not measured and not considered

part of the reaction.

Reading the TST

- The reaction to the TST should be assessed 48 to 72 hours after the
injection by trained health-care worker. Reactions to PPD usually
begin 5 to 6 hours after injection, reach a maximum at 48 to 72 hours,
and subside over a period of a few days. However, positive reactions

often persist for up to 1 week or longer.

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