Allergies commonly tested for are grass and tree pollen, fungal spores and cat and dog. There are tests available for other allergens.
What is an allergy?
When exposed to certain substances some people have an exaggerated immune response. In type 1 allergy, their body produces antibodies, which is its way of preparing to fight an attack. This is called sensitisation. When the body is again exposed to the allergen an allergic reaction occurs. The antibodies stick to the allergen particles. Within minutes this initiates histamine production, which in turn causes a number of what may be unpleasant reactions the body. There may be rashes on the skin, swelling inside the nose, an increased production of nasal secretions and constriction of the respiratory passages. In severe attacks it may become difficult to breath; the blood pressure may drop producing dizziness or collapse.
In type 4 allergy, the reaction is delayed by hours or days and involves white cells and not antibodies. It shows up in the area of skin that has been in contact with the allergen, producing itchy dermatitis.
There are a huge variety of naturally and synthetically occurring allergens which you may be exposed to everyday. Accurate identification of the cause of the allergic reaction is important so that in future it can be avoided. Various tests are available to aid identification.
Once you have been referred by your GP you will need to ring Ashtead Outpatient Department to speak to one of our Outpatient Specialist Nurses. She will take a detailed history regarding the problems you have been experiencing.
Providing it is appropriate and you are not taking any medication which may interfere with the test - you will be offered an appointment.
The skin test is safe and causes little discomfort. It takes about 20 minutes and you will see the result for yourself. We will send a copy of the result to your GP. You will need to arrange a further appointment with your GP to discuss the results.
Skin Prick Test (For Inhaled Allergens)
In this test a small amount of allergen is introduced into the upper layer of skin, usually on the forearm. To enable small children to be more relaxed, the back can be used.
After 20 minutes the site is examined for any sign of reaction. If it has become red and itchy possibly with a white swelling or weal, an allergic reaction may be indicated. The weal should fade within a few hours.
Patch Testing (For Type 4 Allergy)
If this type of test is required your GP must refer you to a Consultant Dermatologist.
There are many substances that can cause inflammation of the skin. Irritant substances are those of which cause inflammation to almost everyone, if applied at sufficient dose for long enough.
Allergens are substances which only cause a reaction to susceptible individuals who are sensitised. Patch testing helps to differentiate between irritants and allergens. It involves taping a specific allergen onto the skin underneath tiny special aluminium discs. The patch will be applied on 1st visit and at 2nd visit at 72 hours the patch will be removed and the skin will be examined for any allergic changes. On the 3rd visit 72 hours later there will be a review by the Consultant Dermatologist. A report will be sent to the GP and Patients may request a copy of the report as well.
Common allergic substances tested by patch testing include, fragrances, lanolin dyes, preservatives, polymers used in nail varnish, adhesives, paints and other cosmetic products and nickel, but there are many others available. The results will be sent to your GP and you will receive a copy.