Thank you for your inquiry.
First, I think it is very important to remember that in anywhere from 60 to 70% of adults who experience an episode of anaphylaxis no cause can be found (1). So, unfortunately, in many instances, no matter how complete the evaluation is, the culprit cannot be identified.
In your particular case, I do feel that your patient experienced an acute anaphylactic reaction in that he met the Sampson criteria (2). By this I mean that he experienced an event due to mast cell/basophil degranulation, whatever the cause.
Having said this, my suggestion to you would be the following:
1. I agree with your strategy of doing a prick-to-prick test with shrimp, and I would also suggest testing to foods in general since he ate other foods that he could not remember.
2. If the test to beef was negative, I would also do a prick-to-prick test with beef.
3. Since reactions to galactose-alpha-1,3-galactose are often delayed (see abstract below), I would order a galactose-alpha-1,3-galactose. This test is available commercially.
4. You might also consider a baseline tryptase if you do not identify a cause, to rule out a mast cell activating disorder.
Finally, if all tests were negative, I also agree with your decision to pursue food challenge in-office.
Thank you again for your inquiry and we hope this response is helpful to you.
1. Webb L and Lieberman P. Anaphylaxis: A Review of 601 Cases. Annals of Allergy, Asthma, and Immunology, July 2006; 97(1):39-43.
2. Sampson HA, et al. Second symposium on the definition and management of anaphylaxis: summary report - second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network Symposium. J Allergy Clin Immunol. 2006;117(2):391-397.
Curr Allergy Asthma Rep. 2013 Feb;13(1):72-7. doi: 10.1007/s11882-012-0315-y.
Delayed Anaphylaxis to Red Meat in Patients with IgE Specific for Galactose alpha-1,3-Galactose (alpha-gal).
Commins SP, Platts-Mills TA.
Department of Internal Medicine & Pediatrics, Division of Allergy and Immunology, University of Virginia Health System, Charlottesville, VA, USA
Anaphylaxis is a severe allergic reaction that can be rapidly progressing and fatal. In instances where the triggering allergen is not known, establishing the etiology of anaphylaxis is pivotal to long-term risk management. Our recent work has identified a novel IgE antibody (Ab) response to a mammalian oligosaccharide epitope, galactose-alpha-1,3-galactose (alpha-gal), that has been associated with two distinct forms of anaphylaxis: (1) immediate onset anaphylaxis during first exposure to intravenous cetuximab, and (2) delayed onset anaphylaxis 3-6 h after ingestion of mammalian food products (e.g., beef and pork). The results of our studies strongly suggest that tick bites are a cause, if not the only significant cause, of IgE Ab responses to alpha-gal in the southern, eastern and central United States. Patients with IgE Ab to alpha-gal continue to emerge and, increasingly, these cases involve children. This IgE Ab response cross-reacts with cat and dog but does not appear to pose a risk for asthma; however, it may impair diagnostic testing in some situations.
Phil Lieberman, M.D.