DIAGNOSIS
Skin Prick and Patch Testing
Skin Prick Testing
The most common way to test for Type I allergy is using a skin prick test (SPT). This is always completed in a clinic or hospital (never at home). A small amount of allergen will be put on a flat part of the body (e.g. inner arm) and a lancet will be used to prick the skin (most patients do not feel anything other than a little pressure); any allergen is then blotted away. After 15 minutes the arm is examined by a medical professional who will ascertain if there has been a reaction. This along with a full medical history is used to diagnose allergies. A list of common allergens that can be used for SPT can be found here (link to list).
Some people are more prone to allergy than others. These people are what is For some people SPT is not appropriate, e.g. those with certain medical conditions or on certain medications that they must take regularly, in which case a blood test can be taken.
What Happens During a Skin Prick Test?
Mark the Forearm
The healthcare professional will mark your forearm with a marker pen, for each allergen to be dropped onto the skin and a mark for a Negative Control (saline solution) and Positive Control (histamine solution).
Allergen Dropped Onto The Forearm
A small droplet of solution for each allergen and control is dropped next to the corresponding mark made in the initial step.
Each Droplet Is Pricked
Using a fresh lancet each time, the HCP will prick through each droplet on the forearm to allow a small amount of the allergen to enter into the skin.
Blot The Area
The forearm is blotted dry, being careful not to wipe as this could cause cross-contamination between each allergen, leading to potential false results.
Wait For The Results
The HCP will tell you to wait 15-20 minutes for the results to form however they will observe in regular intervals to see how the test is progressing.
Read The Results
The HCP will read the reactions and draw around any wheals that have appeared following a reaction. Each wheal will be measured using a wheal gauge.
Discuss The Results
The HCP will discuss the results with you and further/next steps if required.
The Science
Overview
Our suppliers provide test solutions for diagnosing IgE-mediated allergic diseases (Type I, Coombs and Gell). These solutions are made from allergenic raw materials of biological origin, including:
- Pollen
- Epithelia
- Moulds
- Mites
- Dusts
- Foodstuffs
Production Process
- Allergen Extraction
Genuine allergens are isolated using aqueous extraction at physiological pH levels. - Refinement
Diafiltration techniques remove low-molecular-weight irritants. - Characterisation
Allergen bulk extracts are analyzed via physico-chemical and immunological methods, including quantification of major allergens. - Lyophilisation
Bulk extracts are freeze-dried into stable allergen active substances for long-term storage. - Diagnostic Solution Preparation
Allergen active substances are diluted with specific diluents to create ready-to-use diagnostic solutions.
Production Process
The allergen concentration in these solutions is designed to induce distinct allergic skin reactions in sensitised patients, aiding in accurate diagnosis.
Patch Testing
To test for a Type IV allergy the most common way to diagnose is a ‘patch test’. Patch testing is carried out by a clinician and entails having patches pre-loaded with allergens, stuck to your back. Again, this will be carried out in a clinic. You will need to keep the patches in place for a couple of days, you will then have them removed. Your clinician will check the results after a further couple of days.
What Happens During a Patch Test?
The Patches are Applied
Your healthcare provider will stick three patches to your back containing 35 potential allergens. They will also use a pen to mark your back. This helps the results to be read later.
A Covering Panel is Applied
The HCP may add a covering panel which will hold the test in place and will allow you to shower, although bathing is not advised. Speak to your patch tester to see if this protective panel has been used, if not you will need to refrain from showering.*
Patches are Removed
After 48 hours the patch test will be removed. At this point you will be able to take a shower but try to avoid touching/rubbing/soaking the test area.
Results are Read
The results will be read by your healthcare professional a further 24 – 48 hours after the patches have been removed.
* When the patches have been applied, you will be advised to avoid sweating, continue to wear loose-fitting clothing if possible and not to sunbathe or use a UV sunbed whilst you have the patches on or afterwards. You will also need to refrain from taking any medication containing steroids. If you are prescribed steroid medication, you must discuss this with your healthcare professional.
