Skin Testing

Indications


* Screening for a current or past infectious agent (TB, coccidioidomycosis, etc)
* Screening for immune competency (so-called anergy screen) in debillated patients


Materials
* Appropriate antigen (eg, 5 TU PPD), usually 0.1 ml
* A small, short needle (25- to 27-gauge)
* 1 mL syringe
* Alcohol swab

Procedure

1. Skin tests for delayed type hypersensitvity (type IV, tuberculin) are the most commonly administered and interpreted. Allergy tests (immediate wheal and flare) are rarely performed by the student or house officer.
Delayed hypersensitivity (so called because there is a 12-to 36-hour larg time untill a reaction occurs) is caused by activation opf sensitized limphocytes after contact with an antigen. The inflammatory reaction results from direct cytotoxcity and release of lymphokines.

2. The most commonly used site is the flexor surface of the forearm approximately 4 inches below the elbow crease.

3.prep the area with alcohol. With the level up, introduce the needle into the upper layers of skin, but not into the subcutis. Inject 0.1 mL of antigen. The goal is to inject the antigen intradermally. If does properly, you will raise a discrete while bleb approximately 10 mm in diameter. The belb should disappear soon, and no dressing is needed.

4. Mark the test site with a pen, and document the site inthe patient's chart. If multiple tests are being administered, identify each one.