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Iodine "allergy" and fish allergy


Reviewed: February 24, 2020
I recently evaluated a 33 year old woman who is 31 weeks pregnant with a concern of "iodine" allergy. (She is an asthmatic and has allergic rhinitis and amoxil allergy.) She is very anemic and brought in box for Fe tabs which contain Povidine as an inactive ingredient. Pt gives history of anaphylaxis to swordfish and anchioves-and avoids shellfish because of +IgE via blood test done as a child. Pt does not believe she has ever actually ingested shrimp, lobster or other true shellfish. She has had a vitamin as a child from which she vomited and may have had hives-she thought it was due to the "fish oil" in it.

I advised the patient that the allergic component in shellfish (ie shrimp, lobster) is likely tropomyosin and iodine is not the issue. However in my search to find the allergen protein for the finned fish she ingested ie swordfish and anchiovie I am unfortunately not coming up with much. She will be seeing a hematologist also.

May I ask how you would handle such a patient? I did sent her for an immunocap to finned fish and shellfish.Obviously the biggest concern here is the fact that she is pregnant, asthmatic although well controlled and anemic


As I understand your presentation, there are two questions: 1.“iodine allergy” and an iron supplement with povidone; 2. fish allergy with reported anaphylaxis to swordfish and anchovies as well as positive IgE to shrimp or other shellfish.

We still struggle with the burden of “iodine allergy” even among our colleagues. Contact hypersensitivity has been documented to iodine containing antispetics (see Ask The Expert below), but IgE mediated iodine immune responses have not been described and there is no relationship to iodine and fish or shellfish allergy. Nevertheless, some practitioners still equate these problems.

I agree with your reassurance of your patient and I would extend this reassurance concerning the “iodine allergy” and possible the fish allergy. Products made from seafood generally do not contain sufficient quantities of seafood allergen to be an issue, though absolutes in medicine are always susceptible to exceptions. There have been issues raised concerning chondroitin sulfate and shell fish allergy but there is no evidence that IgE binding proteins from shellfish are in chondroitin products (Gray, Heather C., Patricia S. Hutcheson, and Raymond G. Slavin. "Is glucosamine safe in patients with seafood allergy?." Journal of Allergy and Clinical Immunology 114.2 (2004): 459-460// Kelso, John M. "Potential food allergens in medications." Journal of Allergy and Clinical Immunology 133.6 (2014): 1509-1518.//) Taylor, S. L., J. L. Kabourek, and S. L. Hefle. "Fish allergy: fish and products thereof." Journal of Food Science 69.8 (2004): R175-R180). There is one small study of challenging fish allergic subjects with fish oil demonstrating no reactions (Mark, Barry J., Andrew D. Beaty, and Raymond G. Slavin. "Are fish oil supplements safe in finned fish–allergic patients?." Allergy and Asthma Proceedings. Vol. 29. No. 5. OceanSide Publications, Inc, 2008.). Therefore, the iron supplement should be no issue.

In addition to parvalbumin, collagen and tropomyosin may be allergens in select species of fish. These allergens may explain cross reactivity among seafood (the tropomyosin of tilapia has 50% homology with tropomyosin of shrimp) but has no relevance to your concern with iodine (Liu, R., et al. "Tropomyosin from tilapia (Oreochromis mossambicus) as an allergen." Clinical & Experimental Allergy 43.3 (2013): 365-377.). In addition, some fish have apparently specific allergens (Kelso, John M., Richard T. Jones, and John W. Yunginger. "Monospecific allergy to swordfish." Annals of Allergy, Asthma & Immunology 77.3 (1996): 227-228). A free review , although not in the medical peer reviewed literature, than you may find of interest is provided here and a study of cross reactivity to fish are provided in these references (de Martino, Maurizio, et al. "Allergy to different fish species in cod-allergic children: in vivo and in vitro studies." Journal of Allergy and Clinical Immunology 86.6 (1990): 909-914”/ Helbling, Arthur, et al. "Fish allergy: is cross-reactivity among fish species relevant? Double-blind placebo-controlled food challenge studies of fish allergic adults." Annals of Allergy, Asthma & Immunology 83.6 (1999): 517-523.) Finally, apparent fish allergy by history can be the result of contaminants (Consortiumcr, AAITO-IFIACI Anisakis. "Anisakis hypersensitivity in Italy: prevalence and clinical features: a multicenter study." Allergy 66.12 (2011): 1563-1569.).

In summary, I would reassure your patient that “iodine allergy” and her history of fish allergy should have no effect on the decision for her to take a necessary treatment for her anemia, where the benefit clearly outweighs any risk.I would continue to avoid swordfish and anchovy with history of anaphylaxis, pending the results of the specific IgE testing. I am skeptical that there is clinical shellfish allergy but with pregnancy I would not recommend a challenge, even if specific-IgE and skin tests are negative. Providing autoinjector epinephrine would seem prudent in light of anaphylaxis history.

Summary Statement 148: Although asthma is associated with an increased risk of a RCM reaction, specific sensitivity to seafood (which is mediated by IgE directed to proteins) does not further increase this risk. There is no evidence that sensitivity to iodine predisposes patients to RCM reactions. (C)

Potassium iodide “allergy”
Q: 9/24/2013
Can someone be truly allergic to potassium iodide? If so, how common is this allergy and can you test for it? I realize that one should not confound allergy to seafood, radiocontrast media and povidone-iodine with allergy to iodine but I want to know if you see in your practice real allergy to potassium iodide.

Also, since we use iodized salt in the United States, would we not expect to see allergy to iodine more frequently if it really existed independent of excipients that can be present in the potassium iodide tablet or liquid?

A: I am approaching your question as if you were intending the term “allergy” to mean “immediate hypersensitivity.” By that I mean hypersensitivity related to the production of IgE against an allergen and the subsequent degranulation of mast cells and basophils after reexposure to this allergen. This is the type of allergy that causes asthma, rhinitis and anaphylaxis to drugs.

In this case, clearly, as you can see from the abstracts copied below, there are no reports of allergy of this sort to potassium iodide. Contact allergy to iodine containing topical antiseptics can occur through a different mechanism.

Thank you again for your inquiry and we hope this response is helpful to you.

J Allergy Clin Immunol. 2004 Dec;114(6):1395-7.
Risk of severe allergic reactions from the use of potassium iodide for radiation emergencies.
Sicherer SH.
Department of Pediatrics, Mount Sinai School of Medicine, New York, NY 10029, USA.
Potassium iodide (KI) may be prescribed for widespread use in the event of a radiation emergency to prevent the uptake of radioactive iodide by the thyroid gland. The available literature was reviewed and expert opinion sought among members of the Adverse Reactions to Foods and the Adverse Reactions to Drugs and Biologicals Committees of the Academy to assemble evidenced-based conclusions regarding the risks of an allergic reaction to this therapy. This article describes the information leading to the following conclusions: (1) anaphylactoid reactions to radiocontrast media should not be considered evidence of KI allergy, (2) allergic contact dermatitis from iodine-containing antibacterial preparations should not be considered evidence of IgE antibody-mediated KI allergy or sensitivity, (3) IgE antibody-mediated allergy to seafood should not be considered evidence of KI allergy or sensitivity, and (4) physicians should ensure that persons are not allergic to inactive ingredients or components of the KI formulation prescribed.

Ann Fr Anesth Reanim. 2005 Jan;24(1):40-52.
["Iodine allergy": point of view].
[Article in French]
Dewachter P, Tréchot P, Mouton-Faivre C.
Service d'anesthésie-réanimation chirurgicale, CHU, hôpital central, 29, avenue du Maréchal-de-Lattre-de-Tassigny, 54035 Nancy cedex, France.
Objective: The aim of this literature review is to suggest a diagnostic and a preventive attitude in patients having presented an immediate hypersensitivity reaction due to an iodinated drug.
Data Sources: Literature review. Data were searched in the Medline database from 1967 to 2004 in English and French language. Complementary references were selected from the bibliography of selected references or from authors' personal databases. The following key-words were used separately or combined: Hypersensitivity, Immediate; Allergy; Contrast Media; Povidone-Iodine; Iodine; Iodine Compounds; Iodides; Amiodarone; Seafood, Parvalbumins; Tropomyosin.
Study Selection: Randomized studies, epidemiological studies, original articles, clinical cases, and letters to the editor were selected.
Data Synthesis: The implication of iodine has never been demonstrated during allergic hypersensitivity reactions due to iodinated drugs. However, IgE-mediated allergic hypersensitivity reactions have been published with contrast media or iodinated antiseptics and will be described in this development. In a wider sense, allergic hypersensitivity reactions due to seafood are evoked because often improperly considered as a risk factor of allergic reaction to iodinated drugs. The allergenic determinant responsible of patient sensitization is not known for iodinated contrast media, but is probably due to povidone in case of iodine povidone. In fish, the allergen is described as the protein M. There has also been strong immunological evidence that tropomyosin is a cross-reactive allergen among crustaceans and molluscs (shellfishs). In case of hypersensitivity reaction occurring with iodinated drug, an allergological assessment is required to confirm the immune mechanism, to identify the culprit drug or substance and to identify cross-reactivity especially with iodinated contrast media.
Conclusion: Asking a patient if he/she is "allergic to iodine" is a question that should be avoided because its significance is null. A diagnosis of drug allergy, essentially relying on clinical symptoms, biological tests and cutaneous tests, is required to take adequate preventive measures.

Phil Lieberman, M.D.

I hope this information is of some help to you and your patient.

All my best.
Dennis K. Ledford, MD, FAAAA