Indications for seafood challenge with limited clinic history
Question:
4/16/2018
What are the risks of an oral food challenge in a patient with a positive skin prick test, positive immunocap (though much below 99% PPV cut-off of 20 kUa/L for fish), and previous unknown "reaction" to fish?
Patient is in foster care, so although there is a history of a reportedly "reaction" to seafood, the culprit food and nature/severity of the reaction or if resuscitation was required are unknown. Family history is completely unknown, but patient does not have a personal history of atopy (besides possible food allergy).
Current foster family eats a lot of fish and would like the patient to be able to eat fish as well.
SPT to fish mix was positive with wheal of 12mm and flare of 20mm; shellfish mix wheal 3mm.
Immunocap: codfish 2.05 kunits/L, salmon 3.36 kunits/L, tuna 0.58 kunits/L. Crab, shrimp, and clam IgE were negative.
Is the risk of an in-office fish challenge low enough in this patient with the above history and testing?
Answer:
We sought the expert opinion of Dr. Sicherer. See his response below.
The decision to undertake an oral food challenge is complex. Briefly, you are considering the chance of a reaction as well as the risk of the reaction being severe, especially when deciding upon location of the test (office, hospital). Within these parameters, the experience of the physician in managing the challenge and any reaction is of course a consideration, personal comfort included.
Here we are told only that there is a history of a “reaction” to “seafood” with absolutely no other information. Actually, the child’s age is not mentioned either, or how long in foster care, which might inform roughly how long ago this all happened and if it happened in infancy (more allergy resolution) or later in childhood (less resolution). I would be interested to know the saline control sizes for the skin test because the mixed fish was seemingly quite large and the mixed shellfish just “average” but actually it is much smaller than the 7 mm histamine so possibly not significant.
We do not know the food, frequency of reactions, symptoms, etc.. However, the term “seafood” was used and we also may question if this was fish, shellfish or both. At the end of the day “something happened” having to do with “seafood”.
Given that the shellfish serum tests were negative and the skin test was small (especially that it was much smaller than histamine) it would seem more likely that the “seafood” allergy might be finned fish. A food challenge to shrimp would seem warranted, and other shellfish could be allowed if passed, with care not to get cross-contact with finned fish.
Regarding fish, if we conclude that the “seafood” was actually fish (not shellfish), then we do have a history of some level of a reaction to at least some fish that made people have the child avoid “seafood” and now a positive test to fish. If there is not still allergy then it resolved, which is not common for fish. In other words, the chance of some fish allergy seems VERY likely (even though the results were not over 20 kU/L).
Now fish is known as a potent allergen so severity could be significant. The complete lack of atopy as described should mean there is no asthma and since asthma adds severity risk to a reaction (since the lung may more readily respond) that is some good news. Undertaking fish oral food challenges would require comfort on the part of the physician and facility but I would assume a reaction is likely and could be severe, if you were planning to test against one fish after another.
One solution or starting point here seems to be canned tuna. Canning may reduce the allergenicity of the tuna plus the IgE level was lower to tuna. And you know a can of tuna is just tuna, not some other fish. That might be a good start on food challenges. It would seem helpful to skin test to individual fish since it may be that he is allergic to some and not others, or has higher risk to certain ones, although if that is proven, decisions also have to be made about allowing individual fish (avoiding cross contact and mis-identification).
Scott H. Sicherer, MD
Patricia McNally, MD, FAAAAI