The skin prick test has several flaws, prompting researchers to investigate into alternative molecular allergy diagnostic tests.
Skin prick tests involve pricking an extract of a suspected allergen onto the surface of the skin. Redness and swelling at the test site indicate a Type I allergy, which is caused by the antibody IgE. This is currently the preferred method for diagnosing Type I allergies as it is relatively cheap, rapid, and provides visual proof of the allergy, which encourages patient compliance for future testing and therapy. Interestingly, the number of allergens recommended for testing varies between countries: European guidelines suggest testing 18 allergens and the US recommend between 10 and 50.
However, as recently debated in the World Allergy Organization Journal, there are several problems associated with skin prick tests. Various factors including age, body mass, medications, and skin conditions such as eczema can influence the specificity and sensitivity of this test. There is a very small risk that patients may suffer an anaphylactic reaction and there are some concerns that this test can actually induce allergies. In addition, patients with multiple allergies often require several tests or further blood tests to confirm the results.
Efforts have been made to improve the reliability of the skin prick test but this has proved difficult. Problems exist due to differences in the way operators perform the test and record results, and the fact that the results must be interpreted in a way that takes patient characteristics and medical history into account. There have also been calls to standardize and improve the quality of the test components (natural allergen extracts and purified allergens), yet this has proved time-consuming and costly.
These disadvantages have prompted investigations into alternative methods. Over the last 30 years, molecular allergy diagnostic tests have been developed, such as the Immuno-Solid phase Allergen Chip (ISAC). Using biochip technology, a specialized instrument can measure the levels of IgE antibodies in a patient’s blood to approximately 112 purified or recombinant allergens simultaneously. Unlike the allergen extracts used in the skin prick test, recombinant allergens have the benefit of being produced under standardized conditions and are free from contamination.
Molecular allergy diagnostic techniques have been successfully used around the world. For starters, IgE is an effective biomarker: it is reliable, sensitive, and does not interact with medications. In addition, ISAC is highly specific and sensitive and can overcome problems associated with testing allergies in individuals with skin conditions and with multiple allergies. It is also particularly useful for young children, who have a smaller surface area of skin available for skin prick testing, and the elderly, whose skin responses become less reliable.
Unfortunately, molecular allergy diagnostic tests are not routinely offered as a primary Type I allergy screening method. This mainly comes down to cost and lack of professional training. ISAC is usually offered only after the skin prick test and blood testing; therefore, more expenses are incurred by the patient. The extra time associated with interpreting and communicating results may also add to the cost. Despite these issues, the authors recommend screening with ISAC first, followed by skin prick testing only if necessary. If more healthcare professionals were trained in the use and interpretation of the results, it is possible that this method will one day become the primary screening method for Type I allergies.
Written by Natasha Tetlow, PhD
Jensen-Jarolim, E, Jensen AN, Canonica GW. Debates in allergy medicine: Molecular allergy diagnosis with ISAC will replace screenings by skin prick test in the future. World Allergy Organ J. 2017; 10:33. Available from: doi.10.1186/s40413-017-0162-3.