Fish is in the top 8 most common food allergens that cause 90% of all
food-allergic reactions. We are talking about “finned” fish, not
shellfish. Fish allergy is more common in adults than children and
typically a long lasting allergy.
Edible fish are typically in the Osteichthyes class in which there
are hundreds of species. Frequently there is cross-reactivity between
fish species. In fact 95% of fish-allergic patients are sensitized to
the major fish protein allergen called parvalbumin. The major allergens
between cod (Gad c 1) and carp (Cyp c 1) are 68% identical. However,
patients don’t always have clinical reactions to multiple fish depending
on processing (see below).
Is Parvalbumin the same for all fish? No, it varies!
- The amount of parvalbumin varies considerably among fish species
which may explain the intensity and frequency of clinical allergic
reactions to different fish. In a study http://www.ncbi.nlm.nih.gov/pubmed/20559001
evaluating salmon, trout, cod, carp, mackerel, herring, redfish and
tuna there was up to a 100-fold difference in the amount of parvalbumin
in the meat. Tuna had the lowest amount of parvalbumin at <0.05 mg
per gram of meat followed by mackerel at 0.3-0.7 mg. Trout, cod and
salmon had 1-2.5 mg per gram of fish meat compared to carp, redfish, cod
and herring which had the highest amount of parvalbumin at >2.5 mg.
The amount of parvalbumin in cooked samples decreased by 20-60%. This
means that some proteins are considered “heat stable” and
Does smoking or pickling fish affect the allergic potential? Yes.
- In Norway, a study evaluated how different processing affects the
allergenicity of fish proteins. They studied fish that had been smoked,
salted-sugar cured, canned, lye-treated (yummy!) and fermented. They
found that smoked fish had increased IgE (allergic antibody) binding
while chemically processed or pickled herring had much lower or no IgE
binding. It turns out that the processing type was more important than
the fish species, although individual responses varied. Most patients
allergic to cooked fresh salmon or tuna can ingest canned salmon or
tuna without difficulty. Some patients can experience allergic
reactions (asthma) to inhaling airborne fish allergen while fish is
cooking!
Fish Testing
- Allergy skin testing: A negative skin test to fish is very likely to predict that a person is not allergic; however, a positive skin test requires clinical correlation.
- Allergy blood test: At a serum specific IgE level of 20 KUA/L, or higher, there is a 99% chance that the patient will experience an allergic reaction if he/she ingests fish.
- Even though patients with fish allergy may have multiple positive
skin tests to various fish, when they underwent a blinded food challenge
and ate each of these fish separately, 2/3 of patients reacted to 1
fish, 20% of patients reacted to 2 or 3 different fish.
- If you are offered a blood IgG or IgG4 tests for specific
foods including fish, something is “fishy” as controlled scientific
trials do not support these tests to correlate with true allergy. An
IgG level is evidence of previous exposure (such as eating the fish),
not necessarily a true allergy.
At Family Allergy Asthma & Sinus Care, if you have experienced an allergic reaction to fish, we can help.
Fish allergy is tricky; just like trying to catch them! |
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