Norm of Penicillin Skin Test
Absence of immediate wheal and flare.
Usage of Penicillin Skin Test
Determination of hypersensitivity to penicillin after previous history of allergic sensitivity.
Description of Penicillin Skin Test
After a period of time, many people stop expressing IgE sensitivity to beta-lactam antibiotics (that is, penicillin), particularly if the reaction occurred during childhood or while the drug was taken orally. This test is used for individuals with a previous history of hypersensitivity to penicillin and who require the drug to treat a particular infection. By injecting small amounts of Pre-Pen (Kremer-Urban), benzylpenicilloyl polylysine, or benzylpenicillin G intradermally and examining for evidence of an enlarged wheal with erythema, one can identify many individuals at risk for developing anaphylaxis.
Professional Considerations of Penicillin Skin Test
Consent form NOT required.
Allergic reaction to intradermal injection (itching, hives, rash, tight feeling in the throat, shortness of breath, bronchospasm, anaphylaxis, death).
Previous anaphylactic reaction to penicillin.
- Withhold antihistamines for 24–48 hours before the test.
- Emergency readiness: The test should be completed in an area where appropriately trained ACLS personnel and emergency medical equipment are available because of the possibility of anaphylactic reaction.
- Obtain 0.9% saline for the injection, Pre-Pen or benzylpenicillin G, alcohol, tuberculin syringes, and 25-gauge ½-inch needles for intradermal injection.
- Initially prick or scratch the skin on a distal extremity with Pre-Pen or benzylpenicillin G.
- Wait 15 minutes to examine the area for evidence of wheal and flare.
- If these are not evident, proceed with one of the following procedures:
- a. Pre-Pen test: Inject 0.02–0.04 mL of Pre-Pen reagent intradermally to make a 3-mm bleb on the forearm. At the same time, inject the same amount of 0.9% saline intradermally near the same area, making the same-sized bleb for use as a control site. After 15–20 minutes, examine the forearm for wheals. Measure the wheals, if present, in millimeters. A positive result will be >5 mm in diameter, with or without a surrounding erythematous area.
- b. Benzylpenicillin G test: Inject a small bleb of benzylpenicillin G, 100 U/mL, intradermally in the forearm. At the same time, inject the same amount of 0.9% saline intradermally near the same area, making the same-sized bleb for use as a control site. If no reaction occurs after 15–30 minutes, repeat the procedure, using benzylpenicillin G, 1000 U/mL. If no reaction occurs after 15–30 minutes, repeat the procedure using benzylpenicillin G, 10,000 U/mL. A 0.9% saline control should be administered with each successive dose. After 15–20 minutes, examine the forearm for wheals. Measure the wheals, if present, in millimeters. A positive result will be >5 mm in diameter, with or without a surrounding erythematous area.
- c. If the procedure is to be repeated using several strengths of penicillin, start with the lowest concentration.
- Keep the area uncovered and open to air.
Client and Family Teaching
- Call the physician immediately if symptoms of a delayed allergic reaction (listed above, under Risks) occur, and seek immediate medical attention if any difficulty in swallowing or breathing occurs.
- The penicillin skin test allows assessment only for immediate or accelerated hypersensitivity reactions. There is no test to assess for risk of delayed reactions.
- Clients with a positive skin test to penicillin are also generally reactive to first-generation cephalosporins.
Factors That Affect Results
- Recent administration of antihistamines may cause false-negative results.
- A positive skin test indicates a 67%–73% risk of immediate to accelerated reaction to penicillin therapy.
- 2%–6% of clients with negative penicillin skin test results have anaphylactic reactions with the administration of penicillin.
- Repeat skin testing should be performed before reinitiation of penicillin therapy if the initial test was negative and the first course of the drug has been completed.
- It is not necessary to withhold corticosteroids before penicillin skin testing.
- Clients with a negative skin test should still be given penicillin cautiously; IV administration may quickly resensitize the client to the drug.