Richard Warrington discussed penicillin allergy testing:
The lack of access to validated penicillin testing reagents has been a major problem for nearly a decade. The minor antigenic determinants appear to be important for diagnosing penicillin allergy.
Skin test positivity to penicillins has fallen steadily over the last few decades. Frequency of side chain-specific reactions appears to be increasing, compared to major and minor determinants. Oral challenges are needed for beta lactam allergy, given decreased sensitization to major/minor determinants (Bousquet 2007).
If the patient is negative to Pre-Pen and the 3 most common minor determinants, there is a 99% likelihood of tolerating beta-lactams. Bousquet's update to Greenberger protocol suggests side chains as cause of reactions might be missed if following Greenberger's protocol. In other words, amoxicillin could still cause reaction with fully negative penicillin tests, and Bousquet suggests a drug challenge.
Testing with PrePen, pen G and amoxicillin (no MDM) was linked with 98% NPV on oral challenge (Macy 2011). The Macy testing protocol consists of: PrePen, Penicillin G 0.01M, Amoxicillin 0.01M, of 242 patients test 2 were positive, 4 reactions in the skin test negative group.
Re-prescription of penicillin after allergic event was associated with a very low rate of reaction (OR 11.2, but only 1.89% overall) (Apter 2004).
What about skin testing for delayed reactions to drugs? Patch testing is occasionally helpful for morbillform eruptions and contact dermatitis.
Occasionally, intradermal tests will become positive at 24 h to 1 week post-testing, and this often mirrors the onset of the delayed reaction to the drug
Twitter summary made possible by @allergydoc4kidz @DrAnneEllis @IgECPD4
Three allergists did a great job posting updates from the 2012 meeting of the Canadian Society of Allergy and Clinical Immunology (#CSACI): @allergydoc4kidz @DrAnneEllis @IgECPD4. Compared to year 2011, this represents 300% growth in Twitter use by the Canadian allergists. The AAAAI has a larger audience and not surprisingly 30 allergists posted Twitter updates from the 2012 #AAAAI meeting. I used the website “All My Tweets” to review the updated from each allergist, for example: http://www.allmytweets.net/#@IgECPD4
For comparison, here are the tweets from the 2011 #CSACI meeting: http://allergynotes.blogspot.com/search/label/CSACI