Food allergy “screening tests”


IMPORTANT The information provided is of a general nature and should not be used as a substitute for professional advice. If you think you may suffer from an allergic or other disease that requires attention, you should discuss it with your family doctor. The content of the information articles and all illustrations on this website remains the intellectual property of Dr Raymond Mullins and cannot be reproduced without written permission.

Food allergy does not usually run in families

Most of the time, children with food allergy do not have parents with food allergy. If a family has one child with food allergy, however, their brothers and sisters are at a slightly higher risk of having food allergy themselves, although that risk is still relatively low.

Some parents want to have their other children “screened” for food allergy as a guide to whether some foods should be avoided. If the test is negative, that may be reassuring, but does not mean that the child will never develop an allergy in the future.

If their screening test is positive, however, it does not mean that the person definitely has a food allergy. In this situation, a food challenge may be required to settle the question definitively. Interpretation of test results (and whether challenge should be undertaken) should thus be discussed. The most common “screening test” for food allergy in the ~ 300,000 babies born in Australia each year is that the food is tried, and is tolerated or not.

A positive allergy test is not the same as being food allergic

It is important to know that a positive skin or blood allergy tests means that the body’s immune system has produced a response to a food, but sometimes these are irrelevant  “false positives”, especially if the size of the skin test reaction (or blood test equivalent) is small. In other words, the test may be positive yet the person can actually eat the food without a problem. In the HealthNuts study in Melbourne, screening tests for foods in infancy followed by hospital challenge demonstrated that around 50% of test results were false positive tests.

For that reason, it is important to eventually confirm the significance of a positive allergy test (in some circumstances) with a deliberate supervised challenge. In a child with a positive test of uncertain meaning, this is often done around school-entry age (sometimes earlier) under medical supervision.

Should I do a screening test?

There are both advantages and disadvantages to undertaking screening, and it is not encouraged as a routine test because of the high number of irrelevant results. If you wish to undertake screening, therefore, you need be aware that if the issue of food allergy is raised because of a positive test, a challenge is really the only way to settle the question. Certainly if the problem is hay fever or asthma or ongoing (chronic) hives lasting days or weeks at a time, food testing is not indicated as a routine unless the person has a history suggesting that they probably have a food allergy as well.

Last reviewed 4 April 2020