Stomach cramps after moules-frites, or hives after spaghetti alle vongole? Clams, mussels, oysters and scallops are bivalve molluscs, a different group from shrimp and crab. Our test checks your blood for IgE to whole clam, the panel's bivalve marker, as part of 300 allergens and allergen components, next to squid, shrimp, crab and lobster.
Clams are bivalves: molluscs with two shells, like mussels, oysters and scallops. The carpet shell and Manila clams on the panel are the clams sold as vongole. The best-known mollusc allergen is tropomyosin, a heat-stable muscle protein.
Bivalves share similar tropomyosin, so IgE to clam often comes with IgE to mussels or oysters. Mollusc tropomyosin differs more from crustacean tropomyosin, though, so the link to shrimp and crab is weaker and less predictable.
Reactions people describe after eating clams or other molluscs include itching in the mouth, hives, swollen lips, stomach cramps, vomiting and wheezing. They usually start within minutes to two hours.
Swelling of the lips, tongue or throat, trouble breathing or feeling faint after eating is an emergency. Call 112 (EU) or your local emergency number. Do not wait for a test.
Bivalves filter seawater, so a bad batch can carry bacteria, viruses or algal toxins. That causes vomiting and diarrhoea in anyone who eats it, and it is food poisoning, not an allergy. It does not show up as IgE.
A hint: food poisoning often affects others at the same meal and may not repeat with fresh shellfish. An IgE reaction tends to come back each time and often includes itching or hives.
From a finger-prick sample, the lab measures IgE to a whole clam extract. Squid, shrimp (ten markers, including tropomyosin), crab and lobster are on the same panel of 300 allergens and allergen components, together with house dust mite tropomyosin.
Your lab report gives the value a class from Negative to Very high. That shows sensitisation, not a diagnosis. Discuss the result with a doctor before you change your diet.
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One finger-prick sample checks IgE to 300 allergens and allergen components, from birch and peanut to cat and house dust mite. Post it to the lab, and about 5 days after it arrives you get a value for every one. Our plain-English guide shows you how to read them. €399 in total, €1.33 per allergen.
Partly. Clams and mussels are both bivalves with similar tropomyosin, so sensitisation often overlaps. Mussels are not on the panel separately. A doctor can read your clam and squid results together with what you have reacted to.
Yes. Mussels are molluscs and shrimp are crustaceans. Their main allergens are related but not the same, so many people react to one group only. Your report shows both groups separately.
Not necessarily. A bad batch of bivalves can cause food poisoning in anyone. If it keeps happening with fresh shellfish, or comes with itching or hives, a test shows whether your blood has IgE to molluscs.
