Types of allergy testing explained

There are several types of allergy tests, and it is important to understand their effectiveness and diagnostic level before investing in one. 

Skin patch testing 

Where contact dermatitis is involved patch testing is used to discover substances which may be causing symptoms. Diluted allergens are applied to the skin (generally on the back) then results are read. Reactions can be inflamed areas, blisters, or red areas. A neutral control area will be ‘patched’ as well. 

Skin prick testing 

This has been available for many years and is the oldest and most reliable form of allergy testing. This test involves pricking or puncturing the skin and adding a droplet of the allergen to the area. Usually, pet dander, moulds, pollens, and various foods are tested. After 15 minutes have elapsed, the skin is examined to see if there are any reactive areas around the puncture sites such as itchy bumps, spots, and raised rash areas. There will have been a positive control pricked area using histamine, which would show a reactive area response and the other puncture areas are compared to this. 

The negative or neutral control area will be a pricked site with saline or salt water added. 
If a skin prick test is negative for the allergens introduced but the individual has shown allergies, then another test known as an intradermal skin test may be carried out. 
The above forms of testing are accurate but restricted as only a certain number of allergens are tested and there has to be an initial ‘decision’ on what to test. If that decision is ‘barking up the wrong tree’ then it can be fruitless.

Intradermal skin testing

This is a method of injecting a diluted allergen just under the top layer of the skin using a fine needle. This test can sometimes have a positive diagnosis over and above the prick test. Intradermal skin tests however are known to give false positive results so it should not be used when investigating food allergies. 

Blood testing

This is another method of investigating food allergies. The ELISA or ‘enzyme linked immuno absorbant assays’. 

The ELISA test involves binding allergic antibodies in a blood sample to an allergen.  A developer substance is added and a colour change is measured and this result is translated into the level of allergic antibody present in the blood sample.  Reports are very easy to understand and most laboratories send the result accompanied by a GP report (always double check this is the case). A blood sample is taken either through venepuncture or finger prick testing. Venepuncture is the better process as a larger sample of blood is taken for testing.

Home finger prick testing does however suit children where venepuncture has to be carried out by a Paediatric Phlebotomist for those under 16, and waiting times for this can be long.

Hair analysis 

Each hair on our heads remains for between two to six years before falling out. The hair follicle is fed by minute blood vessels and whilst in situ the hair absorbs various chemicals and toxins. Hair analysis is a technique which looks closely at the hair under a microscope. Unfortunately, tests vary from laboratory to laboratory, and it is believed that hair analysis should be used in conjunction with other tests not on its own.  
 
Hair analysis can show drug use such as opioids and better means cannabis and cocaine. The contamination of the drugs can linger for up to three months on each hair. 

It is always wise to double-check the effectiveness of any testing which is done. The price can be very low, but this does not mean you will get the best accuracy. 

Ask a nutritional practitioner or other health professional for recommendations, as they will have information regarding laboratories and testing facilities which are regulated and safe.