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Making sick children better.

Dr John Chapman FRCPCH

Consultant Paediatrician (NHS & Private)

 General Paediatrics, Asthma and Allergy

Book an ISAC Allergy Review

Component testing simplified

Imagine the word PEANUT. It has 6 letters, all different.

Now you become allergic to the word PEANUT. Which letters are you allergic to?

If you are allergic to letters P or N you could have a big reaction. Allergy to letters U and T is not so bad.

If you are Letters A or N allergic, then you might also have allergy to the word BANANA.

Does that make it easier to understand?

How to take a blood allergy test at home.

ISAC 112 Allergy Component testing

What is an allergen component?

OK. Let's start. This might be a bit of a rollercoaster!

When you have Skin Prick Testing (SPT) or specific IgE (RAST) testing you are tested of the whole allergen. Sometimes we use the whole product in testing e.g. a milk prick-prick test. But a food or a plant is more than just one protein.

I will use peanut as an example but this is also true of most of the main things that we are allergic to.

A peanut has proteins which fight off mould (PR10 plant defence proteins), proteins for energy storage (2S albumins) etc, etc. ISAC 112 tests for six different Peanut proteins and it is possible to be allergic to one or more of these.

Why does it matter?

If you have a skin prick test to peanut and you get an 8 mm reaction, you don’t know what protein(s) you are allergic to. You will be labelled peanut allergic with all the anxiety and hassle that that diagnosis carries with it.

Component testing can make the picture a little clearer. Remember also that the history of your initial contact/reaction with Peanut is very relevant.

If you are Peanut PR10 allergic and you eat a peanut, you will probably get an itchy mouth which will settle within minutes perhaps with some antihistamine. No big drama.

If you are Peanut 2S Albumin allergic and you eat a peanut, you may well have an anaphylactic reaction. Big Drama!

I would give much stricter advice to someone who is Peanut 2S Albumin or LTP allergic than someone who is purely PR10 allergic.

I have used peanut as an example but the same is true for many of the things that we are allergic to such as apple, peach, hazelnut and kiwi.

What about Pollen Fruit Syndrome (PFS)?

ISAC 112 testing is excellent for clearly defining the cause of PFS. It includes a number of PR10 proteins and Profilins which can trigger PFS. Whilst, with experience and skin testing, we can infer a diagnosis of PFS, ISAC 112 gives a much clearer answer.

How can I get Component or ISAC 112 testing?

I have teamed up with The Doctors Laboratory (TDL) who can do the ISAC 112 test as well as a huge range of other single component tests. If you are allergic to it, then they probably have a test for it! Ask to find out.

The ISAC 112 test requires such a small amount of blood that it can be done using a home collection kit from drops of blood from a finger-prick. The sample is then posted back to the lab. The result come back within a week.

To read more about ISAC 112 and component testing read on

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