Allergy and intolerance
IgE antilichamen soja
Antibodies against soy protein; shows whether the immune system is sensitive to soy, not whether you get symptoms from it.
Everything about this testWhat it measures
This test measures the amount of IgE antibodies against the proteins in soy in the blood. IgE is the type of antibody that, in an allergic reaction, prompts mast cells to release histamine. The body only makes such antibodies after it has been in contact with the allergen before; this is called sensitization. The result is a number in kU/l; the laboratory states from which value the result counts as positive.
- Sensitization to soy: the body has made IgE antibodies against soy
- Support in looking into a suspected soy allergy, together with the story of the symptoms
- Support in answering whether symptoms after soy products fit an allergy
High
A value above the cut-off means you have IgE antibodies against soy: sensitization. That is not the same as an allergy. Of all commonly used IgE tests, the one for soy gives the most positive results without symptoms. This is due to cross-reactions with peanut and other legumes and with pollen. Doctors mainly see soy allergy in young children with eczema; after one to two years without soy, most of them tolerate soy again. According to the Dutch Society for Clinical Chemistry (NVKC), the height of the result says nothing about how severe a reaction would be, although a clearly higher value does go with a higher chance that there really is an allergy.
Low
A value below the cut-off means that no IgE antibodies against soy were found. A soy allergy that works through IgE is then a lot less likely. A normal result rules out soy allergy less well than for peanut or egg. According to the Dutch medical specialists' guideline (FMS), the protein Gly m 4, which is linked to a birch pollen allergy, is barely present in the test fluid used, so this form of soy allergy can be missed. Symptoms after eating can also have another cause, for example an intolerance or a bowel condition.
If your result is abnormal
The GP mainly looks at the story: which symptoms, how soon after eating and how often. Often a food diary follows, along with temporarily leaving out and then reintroducing the suspected food. If a real allergy is suspected or after a severe reaction, you are referred to an allergist or pediatrician, where a food challenge is done if needed; according to the Dutch medical specialists' guideline (FMS), that test is the gold standard.
Reliability
A positive IgE result shows sensitization, not allergy: it only means there are antibodies, not that you get symptoms from soy. The pooled specificity of the IgE test for soy in the Dutch medical specialists' guideline (FMS) is 38 percent: well over half of the people studied without a soy allergy still test positive. Because a positive result also occurs in people without an allergy, the result can cause confusion when looked at apart from the symptoms. The result can only be interpreted together with the story of the symptoms and, in case of doubt, with a food challenge in hospital.
Limitations
- Cross-reaction with peanut and other legumes often gives a positive result without symptoms.
- Soy allergy linked to a birch pollen allergy (the protein Gly m 4) is often missed with this test.
- You may well tolerate a soy drink or soy product, even with a positive result; only the story of the symptoms counts.
- Laboratories use different measuring methods; results from different labs cannot always be compared one to one.
How common is this
How common soy allergy is in the Netherlands is not known. Children with eczema in whom a food allergy is suspected have a 1 to 4 in 100 chance of a soy allergy. In adults, soy allergy is less common.
Who is this useful for
The result says the most when there has been a clear reaction shortly after eating soy, as an addition to the conversation with the doctor. In people who eat soy normally and have never had an acute reaction to it, a positive result does not mean you are allergic and can lead to avoiding soy unnecessarily. With vague symptoms such as abdominal pain, tiredness or eczema without a clear link to a meal, the test adds little.
Downsides and risks
- A positive result without symptoms easily leads to soy being left out of the diet unnecessarily. That can lead to a shortage of nutrients and, according to Thuisarts.nl, actually increase the chance of an allergy, especially in children.
- A normal result does not rule out symptoms caused by soy: some people with symptoms have no IgE antibodies that can be found in the blood.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results