Allergy Testing

Allergy Testing

Allergy testing is widely advertised on the high street and on marketing websites. There are only 3 validated ways to confirm if IgE allergy exists; Skin prick testing, Specific IgE blood testing and Oral food challenges. I will discuss each of these below.

All other methods which are advertised are not validated and are not supported by the British Society of Allergy and Clinical Immunology. These tests are not scientific and will be unhelpful. You or your child may be told to unnecessarily restrict your diet based on testing which may include hair analysis. This is dangerous as it can cause children to lose their tolerance to foods and allergy may then form. In addition, over-restrictive diets can lead to malnutrition and growth impairment.

Please ensure allergy testing is done by an expert with the knowledge to understand when tests are indicated, choose the correct one and analyse them correctly. Be caution of professionals who are doctors when they are not offering a validated method of allergy testing.

Skin Prick Testing

One of the ways I undertake allergy testing in my clinic is with a skin prick test. This is quick to do and we get answers after 15 minutes! Believe it or not, it is well tolerated by babies, toddlers, children and adults alike! Babies often sleep through the test.

To have the test done, the patient will need to have stopped all anti-histamines 4 days before their clinic appointment. If creams are normally applied to the skin, I would ask that it isn’t put on the arms on the day of the appointment.

Procedure:

  1. The arm is rested on a pillow with the inner surface of the arm facing upwards.
  2. Abbreviations are written on the arm so I know what I’m testing eg. P for Peanut.
  3. Small droplets of solution containing various allergens (substances we are testing) are applied to the arm.
  4. The bubbles of solution are ‘popped’ with a lancet- this feels a bit like you have been poked with a sharp pencil. No blood is drawn.
  5. The solution is wiped away and we wait for 15 minutes.
  6. After 15 minutes, the raised bump is measured and I can then give you information about the likelihood of allergy.
  7. If I do not have a solution of the substance I wish to test; if you have brought the food you are concerned about to clinic then I can prick the substance and then prick the skin. Again, we wait 15 minutes and then see if a raised bump has appeared.

Allergy skin prick tests are safe to do in a clinic setting.

Solutions of allergens eg. grass pollen, milk, egg

Lancets are used to ‘pop’ the bubbles

The raised bumps are measured to determine if allergy exists

Blood Test – Specific IgE Testing

Sometimes allergy skin prick tests are not possible to carry out, for instance, if a child has sensory needs they often do not like this process or if someone is unable to stop their anti-histamine for the test to be carried out. In these circumstances, blood tests can be used to provide us with some answers. A small amount of blood can be sent of and the amount of IgE against each substance measured. A measurement of >0.35 is positive. Blood will be taken by a trained phlebotomist.

Unfortunately, it will take several days for the blood test results to be available so we will arrange a later date to discuss the results and next steps.

Some high street allergy testing centres may send blood samples for analysis but if they are testing IgG and not IgE, then these tests are not validated.

Oral Food Challenge

Oral food challenges are performed in a NHS hospital setting. These are usually done to show that someone has outgrown an allergy in a safe environment. This is performed for those with IgE mediated allergies when it looks like their allergy has resolved – we are usually guided by skin prick tests and IgE blood tests becoming negative. If I think that you or your child needs this done, then we will liase with your GP to request a referral to an allergist.

Alternative Testing

Alternative testing has no proven benefit in the diagnosis of food allergy and
food Intolerance. This may endanger patients via misdiagnosis. An accurate
diagnosis requires detailed clinical assessment by a qualified health care
professional with expertise in Allergy and may include relevant validated
investigations such as specific IgE testing, skin prick testing and oral foods
challenge testing. (follow link for more information from Choosing Wisely and the British Society of Allergy and Clinical Immunology)