Q: When I was 10, I broke out in hives while eating a tuna sandwich. I was tested and diagnosed with an allergy to fin fish – and have avoided fish ever since. Now in my fifties, I did a skin test for salmon with an allergist, and it came back negative! However, I tested positive for cod. Can you be allergic to one or two types of fish but not to all?
Dr. Sharma: Yes, it is possible to be allergic to certain fish and not others. In 2004, Dr. Scott Sicherer and colleagues conducted a study. They found that of 58 patients with fish allergy identified in a national telephone survey, two-thirds reported reactions to multiple fish. However, the remainder reported allergy to only one type.
A more recent study of 35 children with allergy to cod, salmon or mackerel found that almost one-third could tolerate at least one of the three types of fish during an oral food challenge.
Skin or blood tests alone are often not sufficient to identify which fish varieties will cause a reaction.
In a study of 20 codfish-allergic children in Italy, positive skin tests were found in many to eight other types of fish. But several of these children with positive skin tests were known to tolerate the other fish in their diet.
How to Know What to Avoid
For individuals who have had severe reactions to one finned fish, the usual advice is to avoid all finned fish (unless they are currently tolerating others). In cases of milder reactions, skin tests and, if indicated, oral food challenges, may help to clarify if other finned fish can be introduced to the diet.
Be sure to discuss your specific case with your allergist to determine the best plan for you.
If you are able to introduce salmon, it will still be important to watch out at restaurants and seafood markets for cross-contact with other fish.
Dr. Sharma is an allergist, clinical researcher and associate professor of pediatrics. He is Chief of the Division of Allergy and Immunology at Children’s National Medical Center in Washington D.C. and Director of the Food Allergy Program. He co-authors “The Food Allergy Experts” column in Allergic Living’s e-magazine. Questions submitted will be considered for answer in the e-magazine.
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