FAQ’s: Allergy Testing

Is allergy testing accurate in babies?

A better question would be is allergy testing accurate AT ALL!

Allergy testing is extremely limited, typically mainstream practitioners only test for IgE allergies, which are the most commonly linked to anaphylaxis and are mediated by immunoglobulin E. There are lots of other pathways that reactions can take to manifest, through other immunoglobulins, T-Cells, directly through mast cells.

Then there are intolerances, some like lactose can cause typically gastro symptoms.

But other chemical intolerances like histamine, oxalate, glutamate, sulphur (-thiol) and salicylate can cause a whole host of allergic symptoms including but not limited to those which are typical of IgE allergies, like hives, rashes, swelling and even in extreme causes anaphylaxis.

So regardless of if someone has an allergy or an intolerance, they can both be very dangerous conditions and should not be undermined simply because one is called an allergy or an intolerance.

Despite the flaws and drawbacks of allergy testing, it can be worth it to identify if your child has IgE type symptoms as it can be essential in their diagnosis, which bar previous anaphylaxis, is often the easiest way to get a prescription for an epinephrine auto-injector (e.g Jext, EpiPen, Auvi-Q etc.)

What is the difference between IgE and IgG testing?

IgE allergies are typically associated with hives, eczema, asthma anaphylaxis etc.

IgG allergies are typically associated with gastrointestinal symptoms.

Mainstream professionals tend to only test IgE through specific IgE blood tests or skin prick tests. IgG tests can sometimes be purchased online, but are more commonly done by more functional and complementary therapists.

Both have flaws and inaccuracies, but can help different people to varying extents.

What is a skin prick? A scratch test?

A skin prick test is when a prepared dropper sample of a potential trigger is put on the skin and then pricked through, or a fresh food sample is pricked with a pricker, which is then used to prick the skin.

This is often used with children as it gives instant results, typically within 15-30 minute, enabling immediate discussions with the allergist/paediatrician regarding treatment.

They are said to rarely give false negatives, but are said to have a 50-60% chance of a false positive (see FARE link below). Due to this, they are best used in conjunction with Specific IgE tests.

There is an increasing number of reservations regarding the use of skin prick testing, as some research shows skin exposure to foods may be linked to an increased risk of sensitisation to those foods. (See AAAAI link below)

So there are many factors that need to be considered when deciding if you want to consent to skin prick tests or rubbing food samples on skin to assess if they are higher/lower risk of causing IgE type symptoms. Those with a higher risk/history of IgE allergies sometimes prefer to do skin rubbing before food trials so they can avoid premature introductions of foods that might be more likely to cause anaphylaxis.

How old does my baby need to be to get allergy tests done?

This will depend on your healthcare provider. Some are willing to do them from birth depending on symptoms or family history. Others will say they are inaccurate until ** insert 4/6/12/8/24months etc.**; when really they’re always inaccurate. Some suggest that because during infancy and early childhood the immune system matures, causing them to be more likely to grow out of certain allergies are easily, the results between repeat tests can vary more. But that doesn’t make them any less representative of an infant’s immune health at the time of the test, it can just give more hope for quicker improvement between repeat tests.

Blood test and scratch test results are different. Which one should I trust?

Blood tests are more accurate than skin pricks, but essentially both are flawed.

Reaction history, improvements following eliminations, and subsequent trials following complete elimination of a suspected trigger, will always be the most accurate way to determine if a food is a trigger.

My baby got allergy testing done. There were no positives. Does this mean baby has no allergies and I should add all the foods back into my diet?

NO. Your experience matters. If you know your child reacted to something and they had vast improvements following an elimination, then trust your experiences. If you aren’t sure, doing an isolated trial may help. But any test results do not negate your experience to your gut. Unfortunately many professionals put too much faith in test results when generally the tests available are extremely flawed.

We will be seeing an allergist for the first time. What should I expect? What should I ask/bring with me/tell him or her?

Don’t expect them to give you all the answers.

Unfortunately many allergists don’t understand the mechanism that causes reactions through breastmilk. So it can be hard as a mum breastfeeding an allergic infant to get understanding in that respect.

If you want skin prick tests for specific foods, they will often ask you to take samples with you, especially if they are less common triggers, though they often have more common allergen samples.
It can help to take a long a list with you of suspected triggers, known symptoms, significant reactions, goals for the appointment any medications/tests/courses of treatment you would like to discuss. Some mums have a folder with reaction history, others have a simple print off with a list, handwritten can work, though typed can be easier for others to read. Either can make appointments more efficient when you’re trying to juggle care of an infant/toddler with a grown up conversation with a professional. If you have something you can hand to them for them to read through to get a quick history like this, it can help save time from back and forth questions, making it better use of time and less stressful with a child.

Related reading:
AAAAI on sensitisation through skin exposure:
FARE skin-pricks:

ETA. New to me comprehensive article on the **RISKS of SKIN PRICK** allergy testing on sensitisation to food triggers.


Also amazingly comprehensive article on the pathways anaphylactic allergies can take including testing:


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s