Skin prick testing recommendations
Some medications and treatments can interfere with the final results of the skin test.
The following are an indication of the number of days you should avoid the following drugs before an allergy testing by skin prick test is carried out.
- Classical or first-generation antihistamines (Atarax®, Polaramine®) = 10 days
- Second-generation antihistamines (bilastine, ebastine, cetirizine, desloratadine, loratadine, rupatadine, terfenadine) = 5 days
- H2 receptor antagonist antihistamines (cimetidine, famotidine, raditidine) = 1 day
- Topical corticosteroids in the area of Prick Test Dose-Response = 2 weeks
- Oral or parenteral corticosteroids continuous patterns should be avoided for 5 days
- Tranquilising and / or psychoactive drugs = 1 week
Topical nasal or inhaled corticosteroids do not interfere with prick testing and do not require washing or an avoidance period. Neither do antihistamines applied by nasal or ocular route.
To perform the prick-test, a drop of the allergen (extract) we want to study is placed on the inner forearm. Two control samples are also included to ensure the test has been conducted properly – a positive control sample, histamine, which will have a reaction in all patients, and a negative control sample, which is usually a saline solution and should give a negative response.
The skin is then pricked through the drop using the tip of a lancet. After a period of 15- 20 minutes the wheals are read, and are considered positive those with a diameter equal to or greater than 3 mm.
Avoid scratching as it may cause skin irritation and itch even more. If your skin turns red from scratching, it will be difficult to interpret the test results.
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