In fact, the split pea and the green pea are one in the same. The split pea can be either a green pea or a yellow pea. Green split peas are identical to green peas. The difference lies in how they are processed. Both are the seeds of Pisum Sativum. To make a split pea, the green pea is peeled and dried. The skin is removed and a natural split occurs in the cotyledon. The split can be further exaggerated manually or mechanically. One can make split peas out of the green pea or the yellow pea. In any case, the peas are the same, and as noted, the difference is in the processing.
I am not aware of any study that has looked at the antigenic relationship between split pea and the lesser processed green pea or “sweet pea” to which you referred. However, the riper the pea, usually, the more allergenic it becomes. That is because storage albumin proteins increase with ripening. Total IgE-binding capacity thus increases during the process of maturation.
This increase in allergenicity is the only thing that I can think of which might explain the difference between your patient’s reaction to split pea soup versus the ingestion of “sweet peas” or “green peas” as a vegetable.
An allergic reaction to split pea soup has been reported (1), but I have not been able to find any report of a case where split pea soup and not green peas eaten as a vegetable caused such a reaction.
In summary, the split pea and the green pea are identical, differing only in how they are processed. This process, however, itself could possibly explain the fact that your patient reacted to split pea soup, but not the ingestion of peas per se. But this is only a theory, and I have not been able to find anything in the literature to substantiate this conclusion.
From a practical standpoint, unless you wish to verify the reaction with an oral challenge, the only reasonable strategy would be to assume that the theory mentioned above is valid, and avoid the ingestion of split pea products.
Thank you again for your inquiry and we hope this response is helpful to you.
1. Zacharisen MC, Kurup V. Anaphylaxis to beans. J Allergy Clin Immunol 1998;101(4 Pt 1):556-557.
Phil Lieberman, M.D.