Are there any tests?

I have heard a lot about different allergy tests and am
confused. My local supermarket offers tests of this kind,
and a friend has also suggested an ELISA test. Can you
give me any more information about these types of test
and allergy tests in general?
‘Allergy tests’ mean different things to different people, and you
will hear a lot of conflicting information about their use. Broadly
speaking, there are two types of allergy test applicable to skin
disease:
• patch tests;
• skin-prick tests (this type of testing can also be carried out
on blood samples with an ELISA test, but both of these
techniques are testing the same thing).
Patch tests look for evidence of contact eczema (also called
dermatitis), such as is seen in allergy to nickel, chromate, rubber,
dyes, glues or perfumes. This is a delayed allergy that sometimes
develops after repeated exposure to a substance. Contact eczemais uncommon in children, perhaps because they have not had
enough exposure to these allergens, so patch tests are not needed
(or indeed helpful) in uncomplicated atopic eczema in childhood.
Patch tests are complicated to do and interpret (they are carried
out only by specialist dermatologists) but are useful in investigating
certain types of eczema – such as isolated hand eczema, especially
in people with certain jobs, for example hairdressers, builders and
nurses.
Skin-prick tests (or ELISA tests) look for an immediate type of
allergy (type 1 allergy). There are hundreds of allergens that can
be used in these tests, but the common ones are pollens (grass and
tree), dog fur, cat fur, house dust mite, egg, milk, fish and nuts.
They can be useful in detecting relevant allergens in asthma, food
intolerance and hay fever. They do not, however, provide much, if
any, useful information in atopic eczema, and most experts in
childhood eczema now realise this. The majority of children with
eczema have multiple positive results to the skin-prick test, and
these are difficult to interpret in any useful way. Children’s skin
seems hyperreactive to many substances. Although some doctors
still do these tests, we believe that it is unjustified to inflict 15
pin-pricks or a blood test on a young child with atopic eczema if
it is not going to provide any practical information in helping to
manage the eczema. These tests do not help in deciding whether
a certain food might make eczema worse and, if they are wrongly
interpreted, can cause problems if nutritional foods are
unnecessarily excluded.