Thread by @AllergyKidsDoc

Today's thread will discuss allergy testing, which is surrounded by rampant misinformation, misinterpretation, and poor understanding.

For this thread, allergy tests = skin prick, intradermal and blood IgE tests. These all evaluate for the presence of allergen specific IgE.

Allergy tests cannot diagnose non-IgE conditions;if you have chronic GI complaints w/o identifiable trigger - this is not caused by IgE allergy. Thus, allergy tests are not useful.

Allergy tests are not screening tests - cannot just 'see what shows up' huffpost.com/entry/read-thi…

Skin prick tests introduce a small amount of allergen (food, pollen, etc) to the allergy cells in the skin.

If IgE is present, a red, itchy bump will appear in ~15 min.

The SIZE of the bump indicates the LIKELIHOOD of allergy being present, according to the clinical HISTORY.

Allergy skin tests must always include a negative (saline) and positive (histamine) control. The allergens should then be compared to these controls.

People with chronic hives, sensitive skin, etc can have nonspecific irritation = neg control pops up & tests cant be interpreted

Serum IgE tests measure the amount of allergen specific IgE in the blood stream.

The level indicates the LIKELIHOOD of allergy being present, according to the clinical HISTORY.

The 'classes' are meaningless = ignore.
Levels mean different things for different allergens.

Both skin prick & blood IgE tests very reliable when used properly and interpreted in the context of the clinical history.
Negative predictive value very high.
But...false positives common.

The mere detection of IgE does not diagnose allergy! Long read: kidswithfoodallergies.org/page/food-alle…

There is no minimum age when allergy tests become reliable. If you're old enough to have IgE mediated allergy, you're old enough to have an IgE test confirming that allergy.

Tests often negative in young children because symptoms are not due to allergy.

Medications can interfere with skin prick testing but not blood IgE tests.

Skin prick measures histamine response to allergen. Meds that block histamine, i.e. antihistamines, should be stopped ~5 days before testing. This does not include asthma inhalers.

Neither skin prick or blood IgE tests predict severity of future reactions. New component tests also do not predict severity, only likelihood of reaction vs cross-reactivity with pollen.

There is no such thing as a test saying "I'm deathly allergic to ___"

There are exactly ZERO validated tests to look for 'food sensitivity'.

At home testing, IgG testing, muscle tests, MRT, hair analysis, etc have no evidence to support their use. Great read by @john_damianos in-training.org/diy-medicine-1…

Allergy tests are not pregnancy tests.

Results are not "positive" or "negative".

They can only be used to help determine likelihood of allergy being present.

A detailed clinical history is the most important test.

If someone orders dozens of tests without history = red flag.

Hopefully this thread addresses some common misconceptions surrounding allergy testing.

As always, there are WAY more details than can be addressed through a Twitter thread.

When in doubt, see a board certified allergist who can discuss YOUR personal health.