| Where It's Done | Who Does It | How Long It Takes | Discomfort/Pain |
| Doctor's office, commercial laboratory, or hospital. | Doctor, nurse, or lab technician; doctor must be present in testing area. | 15-20 minutes. | Minor discomfort from needle stick. |
| Results Ready When | Special Equipment | Risks/Complications | Average Cost |
| Immediately. | Extracts of penicillin in a saline solution; needle and syringe. | Minor bleeding under the skin, itching, skin irritation, and slight risk of a widespread allergic reaction (less than 1% of cases). Should not be performed in people who have prevously had a severe reaction to penicillin. | $-$$ (depending on number of tests). |
Skin tests for penicillin allergy.
Purpose- To identify people at risk of a severe allergic reaction to penicillin.
- To determine the safety of penicillin and its derivatives for those who have had allergies to antibiotics.
If an allergy is present, a small amount of penicillin will produce a red, raised spot, called a wheal, at the test site.
PreparationFor several days before the test, avoid taking antihistamines, hydroxyzine (Atarax), tricyclic antidepressants, phenothiazines, and other medications that may block an allergic response.
Test procedureReaction to penicillin is assessed first by a prick test, then by an intradermal test (see above).
After the test- You will be asked to wait 20 to 30 minutes to be sure there is no severe allergic reaction.
- Do not cover the injection site, but keep it clean until it completely heals.
- Notify the doctor immediately if you experience light-headedness, wheezing, severe itching, or shortness of breath later in the day.
- Poor circulation under the skin may blunt the results in the scratch, prick, and puncture tests.
- Antihistamines, tricyclic antidepressants, phenothiazines, and other drugs may block allergic reactions.
- Overall health: Dialysis or widespread cancer may blunt the allergic response.
The presence of a red, raised wheal larger than 5 millimeters (a little less than 1/4 of an inch) in diameter indicates allergy to penicillin. The larger the wheal, the greater the severity of the allergy.
AdvantagesIf you have no history of penicillin allergy, a negative test virtually rules out the risk of a life-threatening reaction to penicillin-type antibiotics.
Disadvantages- Minor reactions, such as rash and itching, may occur during penicillin therapy, even if a penicillin allergy test was negative.
- Test results do not apply to other classes of antibiotics.
- The test assesses only allergic reactions caused by IgE antibodies (see above).
- Such adverse effects as serum sickness (most commonly, hives, pain, and swelling) and drug fever (a high temperature due to a drug reaction) may still occur, even if penicillin skin test is negative.
- A negative result in the absence of symptoms is sufficient to rule out penicillin allergy; no further testing is required.
- If the test is positive, you should not be treated with penicillin if possible. If penicillin must be given, you can be desensitized in the hospital.
