How does our doctor know that my child’s rash is eczema?

As there are no specific tests for most types of eczema, your doctor
will have reached a diagnosis on what we call ‘clinical grounds’.
This means taking a careful history of the problem and any family
history of eczema, asthma or hay fever. Examination of the skin
will add to the clues in the history, allowing a diagnosis to be made.
Some people with atopic eczema may have abnormal blood tests,
such as high levels of an antibody called immunoglobulin E (IgE).
Antibodies are chemicals made by the body as a defence against
infection but are also involved in allergic reactions. Specific
allergens (the causes or triggers of allergy) can lead to high levels
of linked IgE, which can be measured by a blood test called an
ELISA test. (This is discussed in Chapter 2 under allergy testing.)
These tests do not, however, diagnose atopic eczema as you can
have abnormal tests and never develop eczema, or have normal
IgE levels and very definite eczema.