This test measures specific IgE attached to cells in the skin
important in allergies called "mast" cells.
Skin prick testing is usually the first test recommended when an
allergy is suspected. The advantages are that it is a simple, quick test
(providing results within 15-20 minutes) .It can give useful information in all
forms of allergy, and is appropriate for inhaled and ingested (eaten) allergies.
The skin prick test introduces such a tiny amount of allergen into
the skin that testing is quite safe, and almost any age group can be tested.
Where there has been a clear anaphylactic (shock) reaction to a specific
allergen ingested then skin testing may not be appropriate.
These tests can be carried out on all age groups including babies,
although the response will be considerably smaller than in an adult.
• It is usually carried out on the inner forearm, but if the patient has bad
eczema the test can be performed on the back .
• Ideally the allergens to be selected should be in accordance with the
patient's history
• As few as 3 or 4 or up to about 25 allergens can be tested
• The arm is coded with a marker pen for the allergens to be tested
• A drop of the allergen (extract) solution is placed by each code
The skin is then pricked through the drop using the tip of a
lancet. This can feel a little uncomfortable but should not be painful.
With a Positive Reaction to an allergen the skin becomes itchy
within a few minutes and then becomes red and swollen with a "weal" in the
centre (very much like the reaction to a nettle sting).
The weal has a raised edge, which slowly expands to reach its maximum size in
about 15-20 minutes. The size of the weal varies with the average being 3-5 mm
in diameter, and it clears for most people within an hour. The size of the weal
does not indicate the severity of symptoms. The test tells us that a level of
anti-bodies are /or are not present which may be causing your symptoms.
Also included in skin testing is a negative and positive control:
The negative control is a saline (salt-water) solution, to which a response is
not expected. If however a patient reacts to a negative control, then this will
indicate that the skin is, for what ever reason, extremely sensitive and that
the results need to be interpreted with the utmost care.
The positive control solution contains histamine, to which
everyone is expected to react. Failure to do so could mean that medicines the
sufferer is taking could block the response to the histamine and allergens.
Patients will be asked to avoid taking some anti histamines, about 6 weeks prior
to the test and some other medicines for about 5-6 days.
A negative response to skin prick testing usually indicates that
the patient is not sensitive to that allergen. Negative reactions may occur if
the patient is taking anti-histamines or medication that block the effect of
histamine. Also the skin in some elderly people may not be capable of reacting.
For reasons which we do not yet fully understand skin prick testing with food
allergens is less reliable than with some other allergens such as dust and
pollens, so false negative reactions can occur.
Allergy Tests
Skin Prick Test from £140
Blood Test (IgE antibodies) from £40
Consultation Only from £35
Food Intolerance Test from £70
Please contact us on 020 7359 1126 / 020 7226 2780 to make an appointment or for
further information about our services.
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