Public Health Analysis South Africa

How reliable exactly are food-intolerance blood tests?

Food intolerance blood tests are designed to detect IgG antibodies against specific foods. However, our body naturally produces these antibodies in response to the food we consume, which raises questions about the reliability of these tests.
Source: Supplied. Vilnius University Life Sciences Centre (VU LSC) researcher Rasa Petraityte-Burneikiene.
Source: Supplied. Vilnius University Life Sciences Centre (VU LSC) researcher Rasa Petraityte-Burneikiene.

This is according to Vilnius University Life Sciences Centre (VU LSC) researcher Rasa Petraitytė-Burneikienė, whose laboratory develops critical components for allergy tests.

The researcher explains that her group at VU LSC synthesises recombinant allergens, which are crucial in identifying various allergies, including food allergies (such as nuts and shrimp), house dust mite, pet allergens, and insect-venom allergies:

We insert allergen DNA into bacteria or yeast, and they produce allergens. These are then purified, characterised, and evaluated for their diagnostic suitability, Petraitytė-Burneikienė states.

Developing allergy tests is a complex process. Identifying the allergy-causing molecule of a specific protein is the first step.

Then, the development involves optimising performance and assessing accuracy and reliability, considering the physico-chemical properties of the allergenic molecule. Sensitivity and specificity evaluations are essential to identify allergies and minimise false positives or negatives

Skin-prick test limitations

Regarding the accuracy of skin-prick allergy tests, Petraitytė-Burneikienė acknowledges their popularity, quick results, and cost-effectiveness but notes that false-positive or false-negative results can occur.

For instance, cross-reactivity can lead to false positives, where a person may react to a similar protein in a different allergen. False negatives might necessitate additional molecular tests to detect specific IgE antibodies.

In addition, skin-prick tests may fail due to the type of allergen extract used. Allergen extracts are protein mixtures prepared from, for example, certain foods, dust mites, pet epithelial cells, or plant pollen.

Source: Supplied. Rasa Petraityte-Burneikiene, working in her lab at Vilnius University Life Sciences Centre.
Source: Supplied. Rasa Petraityte-Burneikiene, working in her lab at Vilnius University Life Sciences Centre.

"The amount of protein in the extracts can vary significantly because the extract may not contain the allergenic protein at all, so we will not detect an allergy," says the VU scholar.

Therefore, according to her, it may be necessary to conduct additional tests, such as a blood test, to check for IgE antibodies to ensure the accuracy of the results.

Recombinant allergen proteins — the ones she creates in her laboratory — are also required to detect specific IgE antibodies in blood tests.

Blood-test constraints

Petraitytė-Burneikienė highlights that blood tests for detecting IgE antibodies offer a quantitative assessment of sensitisation to multiple allergens and are useful for individuals with multiple allergies. However, these tests can also yield false results.

"IgE levels alone do not necessarily indicate an allergy if you do not experience any allergy symptoms. This is called asymptomatic sensitisation. In the case of asymptomatic sensitisation, the human body produces IgE antibodies in response to the allergen.

"However, when exposed to that allergen, it has no allergy symptoms because the body has mechanisms to regulate the immune response.

"These mechanisms can sometimes suppress allergic reactions, even in cases of elevated IgE levels. In addition, allergic reactions occur when the immune response exceeds a certain threshold. Blood tests to identify food intolerance are critical," says the researcher.

"The utility and reliability of these tests are questionable because IgG antibodies are a natural immune response to food antigens, not indicators of food intolerance or allergy. The presence of IgG antibodies simply shows exposure to certain foods, not an adverse reaction," Petraitytė-Burneikienė asserts.

"This is distinct from tests for digestive enzyme deficiencies, which are true food intolerances and are determined through different methods such as genetic or PCR tests."

In conclusion, Petraitytė-Burneikienė emphasises the importance of consulting with an allergist for accurate allergy diagnosis and treatment. Only an allergist can properly evaluate your condition and interpret blood-test results to identify allergies, she advises.

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