An Allergy Screen (Antibiotics) Blood Test is used to detect allergic reactions to specific antibiotics by measuring IgE antibodies in the blood. Antibiotic allergies are common, with symptoms ranging from mild rashes to severe reactions like anaphylaxis. Identifying an allergy to a specific antibiotic is crucial for preventing serious reactions and for guiding future treatment choices.
Purpose of Antibiotic Allergy Blood Tests
- To identify if a person has an IgE-mediated allergic response to specific antibiotics, such as penicillin or cephalosporins.
- To differentiate between true allergic reactions and other non-allergic side effects (e.g., gastrointestinal upset).
- To help avoid unnecessary avoidance of antibiotics due to misdiagnosed allergies.
Types of Antibiotic Allergy Blood Tests
- Specific IgE Testing for Antibiotics:
- Measures the presence of IgE antibodies to specific antibiotics.
- Common antibiotics tested for IgE-mediated allergies include:
- Amoxicilloyl
- Ampicilloyl
- Cefaclor
- Pen G
- Pen V
- A positive result indicates that the immune system has produced antibodies against the antibiotic, suggesting a potential allergy.
- Penicillin-Specific IgE Testing:
- This test is particularly important for people who report a history of penicillin allergy, as many people outgrow penicillin allergies over time.
- A negative test may indicate that the person no longer has an allergy, allowing safe use of penicillin.
- Component-Resolved Diagnostics (CRD):
- In some cases, this more advanced form of testing may be used to identify specific components within the antibiotic responsible for the allergic reaction.
- This is less common but may be useful when cross-reactivity between different drugs is suspected.
Limitations of the Blood Test
- False Negatives: Sometimes, IgE-mediated allergies are not detected by blood tests, even when a true allergic reaction has occurred. This can happen if the patient has low levels of IgE or if the allergy is not IgE-mediated.
- Non-IgE-Mediated Reactions: Some antibiotic allergies are not mediated by IgE but rather by other immune pathways (e.g., delayed hypersensitivity reactions like Stevens-Johnson Syndrome). These will not be detected by IgE blood tests.
- Skin Testing: In some cases, blood tests are used in conjunction with skin testing to get a more complete picture of the allergy.
Interpreting Results
- Class 0: No detectable specific IgE; unlikely to be allergic.
- Class 1-6: Increasing levels of IgE indicate increasing likelihood of an allergic reaction, with Class 6 representing the highest sensitivity.
- Even with a positive blood test, a clinical history of symptoms and reactions to the antibiotic is critical to confirm a diagnosis of allergy.
Diagnosis and Management
- Oral Challenge Test:
- After a negative blood or skin test, an oral drug challenge may be performed under medical supervision. The patient is given small, increasing doses of the suspected antibiotic to confirm that it is safe to take.
- Desensitization:
- In cases where the patient is allergic to a crucial antibiotic (e.g., penicillin) and no alternatives are suitable, desensitization may be performed. This involves administering small, increasing doses of the antibiotic under close supervision until the patient can tolerate the drug.
- Avoidance:
- If the test confirms an allergy, the patient must avoid the antibiotic. Doctors will provide alternatives and may recommend carrying emergency medications like antihistamines or epinephrine (EpiPen) for severe reactions.
When Is Antibiotic Allergy Testing Recommended?
- If someone experiences hives, swelling, difficulty breathing, or anaphylaxis after taking an antibiotic.
- If a patient has a history of antibiotic allergy but is unsure of the specifics.
- Before starting a course of antibiotics when the patient has a history of severe allergic reactions.
An allergy screen for antibiotics provides valuable information for managing treatment and ensuring patient safety.
Results – 2 days from Laboratory receiving sample
