Phytohaemagglutinin (Red Kidney Bean Poisoning)

Phytohaemagglutinin (Kidney Bean Lectin) is a compound that causes red kidney bean poisoning (kinkoti bean poisoning, and possibly other names). Red kidney bean poisoning is most often caused by consuming raw or undercooked kidney beans.

What are the symptoms of red kidney bean poisoning?

The onset time from consumption of raw or undercooked kidney beans to symptoms varies from between 1 to 3 hours. Onset is usually marked by extreme nausea, followed by vomiting, which may be very severe. Diarrhea develops somewhat later (from one to a few hours), and some persons report abdominal pain. Some persons have been hospitalized, but recovery is usually rapid (3 - 4 h after onset of symptoms) and spontaneous.

How is the illness diagnosed?

Diagnosis is made on the basis of symptoms, food history, and the exclusion of other rapid onset food poisoning agents (e.g., Bacillus cereus, Staphylococcus aureus, arsenic, mercury, lead, and cyanide).

Can other beans cause the illness?

Yes. Phytohaemagglutinin, the presumed toxic agent, is found in many species of beans, but it is in highest concentration in red kidney beans ( Phaseolus vulgaris ). The unit of toxin measure is the hemagglutinating unit (hau). Raw kidney beans contain from 20,000 to 70,000 hau, while fully cooked beans contain from 200 to 400 hau. White kidney beans, another variety of Phaseolus vulgaris, contain about one-third the amount of toxin as the red variety; broad beans (Vicia faba) contain 5 to 10% the amount that red kidney beans contain. The syndrome is usually caused by the ingestion of raw, soaked kidney beans, either alone or in salads or casseroles. As few as four or five raw beans can trigger symptoms. Several outbreaks have been associated with "slow cookers" or crock pots, or in casseroles which had not reached a high enough internal temperature to destroy the glycoprotein lectin. It has been shown that heating to 80 degrees Celsius (175 degrees Fahrenheit) may potentiate the toxicity five-fold, so that these beans are more toxic than if eaten raw. In studies of casseroles cooked in slow cookers, internal temperatures often did not exceed 75 degrees Celsius (170 degrees Fahrenheit).

How common is red kidney bean poisoning?

This syndrome has occurred in the United Kingdom with some regularity. Reports of this syndrome in the United States are anecdotal and have not been formally published.

Who is susceptible to the illness?

All persons, regardless of age or gender, appear to be equally susceptible. The severity is related only to the dose ingested.