Skin Prick Testing Changes

The Pathlab skin prick testing request form has been updated and is available to download:

As before, the form is electronically fillable, but the patient consent portion will now be provided by Pathlab and completed at the time of testing. Aeroallergens will now always be performed as a panel, and only when clinically indicated due to allergic rhinitis/conjunctivitis or asthma.

The clinical indications no longer include eczema. Eczema is primarily a skin-barrier problem. It is associated with rhinitis, asthma, and food allergies and is part of the allergic march; however, it is not an allergy. The latest understanding is that food allergy in infants may result from exposure to food allergens through the broken skin of eczema, hence the association. The food allergy is therefore secondary to the eczema rather than the cause of it. Some aeroallergens may exacerbate eczema, for example, house dust mite; but house dust mite allergy is primarily associated with rhinitis and asthma.

Skin prick testing for a range of foods does not provide useful information. Where there has been an acute allergic reaction immediately following a food allergen, for example, peanut, then only the specific food consumed should be tested. History is the most important aspect to determining whether a food allergy is likely, for example, has the individual developed acute urticaria soon after eating the food? Skin testing can confirm a food allergy to that particular food. Testing to a range of foods is not indicated, just the implicated food should be tested.

Positive responses to allergens in the absence of acute allergy symptoms following exposure is called sensitisation. This does not equate with allergy. Avoidance of a food that someone is sensitised to, but has been eating without problems, may actually result in the development of an allergy. Random testing of food allergens in someone with eczema can lead to multiple food exclusions due to sensitisation misinterpreted as allergy. This can result in nutritional deficiencies and food anxiety.

Chronic urticaria is also not due to an allergy. Food allergy and aeroallergen allergy do not cause chronic urticaria. Skin prick testing in chronic urticaria is therefore not indicated. Anxiety about allergies is common in this scenario and, once more, history and patient reassurance is most important.

The best test for allergy is what happens immediately following exposure. If peanuts are consumed without symptoms there is no indication of an allergy and testing should not be performed.