Quick Facts
- Sample: Blood (serum)
- Fasting: Not required
- Turn-around: 6-8 business days. May take longer based on weather, holiday or lab delays.
Benefits
- Confidential results - order online, get tested locally, receive expert interpretation
- Safer antibiotic choices - identify true penicillin allergy to avoid unnecessary broad-spectrum antibiotics
- Minimal-risk testing - blood draw is safer than skin testing or drug challenge procedures
- Prevent severe reactions - early detection reduces risk of life-threatening anaphylaxis during future treatment
- Improve antibiotic stewardship - accurate diagnosis helps preserve effective penicillin-class medications when safe
Who Is This Test For?
- Individuals with history of immediate reactions (hives, swelling, breathing difficulty) after taking penicillin
- Patients needing preoperative allergy screening before planned surgeries or procedures
- Those told to avoid penicillin but unsure if they have true allergy
- Health-conscious individuals seeking direct lab access without physician referral
- Anyone wanting to clarify whether past symptoms were allergic reactions or common side effects
How It Works – Just 3 Steps
- Order online - purchase your test kit through our secure platform with no appointment needed.
- Visit a local lab - bring your test requisition to a nearby walk-in draw site for quick blood collection.
- Review your results - receive confidential findings in your secure online portal within 6-8 business days.
FAQ
What does this test measure? This test detects specific IgE antibodies to penicillin G in your blood, indicating immune system sensitization to this antibiotic.
Can I eat before the test? No fasting is required—eat and drink normally before your blood draw appointment.
When is the best time to get tested? Ideally within 4–6 weeks up to 12 months after your suspected allergic reaction for maximum sensitivity (ASCIA 2020).
Will this test definitively confirm or rule out penicillin allergy? Not completely—sensitivity ranges 30–50%, so negative results don't exclude allergy; positive results require clinical correlation (Mayo Clinic 2024).
What if my results are positive? A positive result means you're sensitized to penicillin G; consult your healthcare provider about skin testing or drug challenge for confirmation.
Should I stop taking penicillin before the test? Never stop prescribed antibiotics without medical guidance—discuss testing timing with your provider if currently on treatment.
More Details
What is the purpose of this test?
This Penicillin G Allergy IgE Blood Test measures specific IgE antibody levels in your blood to help detect an allergic immune response to penicillin G (benzathine penicillin). When your body views penicillin as a threat, it produces IgE antibodies that trigger histamine release, causing allergic symptoms ranging from mild skin reactions to severe anaphylaxis. This test uses ImmunoCAP® or similar fluorescence enzyme immunoassay technology to quantitatively measure these antibodies, helping clinicians and patients assess allergy risk. Accurate identification of true penicillin allergy guides safer antibiotic selection and reduces unnecessary avoidance of effective penicillin-class medications (CDC 2025).
Who would benefit from this test?
This test is particularly valuable for patients with suspected immediate (Type I) hypersensitivity reactions to penicillin. You may benefit if you've experienced symptoms like hives, swelling, breathing difficulty, or anaphylaxis within minutes to hours after penicillin exposure. It's also helpful for individuals needing preoperative allergy screening, those told to avoid penicillin without confirmation testing, or anyone wanting to distinguish between true allergic reactions and common medication side effects. Since only 5.2% of patients with suspected penicillin reactions actually have elevated specific IgE (PMC 2024), testing helps identify who truly needs to avoid this essential antibiotic class.
When should I order a Penicillin G Allergy IgE Blood Test?
Order this test if you've experienced potential allergic symptoms after taking penicillin, including itching, hives, skin rash, swelling, fever, itchy watery eyes, runny nose, shortness of breath, wheezing, or anaphylaxis. For optimal accuracy, test within 4–6 weeks up to 12 months after your suspected reaction, as sensitivity decreases significantly over time (ASCIA 2020). The test is also valuable before planned surgeries or procedures requiring antibiotic prophylaxis. Since penicillin side effects (muscle spasms, injection site pain, chills, joint pain, upset stomach) closely resemble allergic reactions, testing helps clarify whether you experienced true allergy or common adverse effects.
How do I interpret the results?
Your results will indicate whether specific IgE antibodies to penicillin G were detected. Use this interpretation guide:
Positive
- What it means: IgE antibodies detected; sensitization confirmed
- Typical action: Consult provider for skin testing or drug challenge confirmation; avoid penicillin until evaluated
Negative
- What it means: No IgE antibodies detected at this time
- Typical action: Does not exclude allergy; discuss further testing if clinical suspicion remains high
Equivocal
- What it means: Borderline or indeterminate result
- Typical action: Repeat testing or proceed to skin testing for clarification
Remember: A positive result indicates sensitization but doesn't predict reaction severity, while a negative result doesn't guarantee safety—clinical correlation is essential (Mayo Clinic 2024).
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
Pre-test preparation
No fasting or special dietary restrictions are required before this blood test. For maximum sensitivity, schedule your test within 4–6 weeks up to 12 months after your suspected allergic reaction. If you're currently taking antihistamines or corticosteroids, these medications do not typically interfere with blood IgE testing (unlike skin testing). However, inform the laboratory of all medications you're taking. Your blood will be drawn into serum separator tubes, then promptly separated and shipped refrigerated to the testing laboratory using ImmunoCAP® or similar technology (AAAAI 2025).
How often should I get tested?
Retesting frequency depends on your clinical situation and previous results:
Initial suspected reaction
- Suggested interval: Once, ideally within 4–12 months of reaction
Negative result with ongoing symptoms
- Suggested interval: Consult provider; proceed to skin testing rather than retest blood
Positive result, awaiting confirmation
- Suggested interval: No repeat needed; proceed to skin testing or drug challenge
After successful desensitization
- Suggested interval: Not typically repeated; clinical monitoring preferred
Years after last reaction, considering re-exposure
- Suggested interval: May retest if considering drug challenge under supervision
Why early detection matters
Accurate penicillin allergy identification is critical for patient safety and antibiotic stewardship. Approximately 10% of the population reports penicillin allergy, yet fewer than 10% of these individuals have true IgE-mediated allergy. Mislabeled penicillin allergy leads to unnecessary use of broad-spectrum antibiotics, increasing risks of antibiotic resistance, Clostridioides difficile infection, treatment failures, and higher healthcare costs. Conversely, unrecognized true allergy can result in life-threatening anaphylaxis during treatment. Early, accurate testing helps preserve effective penicillin-class antibiotics when safe while protecting truly allergic individuals from dangerous re-exposure (CDC 2025).
Related tests you may consider
Penicillin V Allergy IgE Blood Test - Measures IgE antibody levels in the blood to help detect an allergy to penicillin V.
Immunoglobulin E Blood Test, Total, IgE - Measures the total IgE antibody levels in the blood to assess the likelihood of experiencing allergic reactions.
20 Antibiotics/Anti-Inflammatory Agents - ALCAT Test Kit - Identifies potential sensitivities or intolerances to 20 commonly prescribed antibiotics and anti-inflammatory medications.
