The technique involves introducing a small amount of allergen under the outer layers of the skin using a needle or lancet and reading the size of the wheal that appears in the 15 minutes after the test is applied. They do not require a laboratory and do not involve taking blood. The technology remains expensive and is not widely used in epidemiologic studies.Īn alternative method of identifying sensitized individuals is to undertake skin-prick tests. Microchip technology and the development of recombinant and purified allergens have enabled testing for several allergens simultaneously and allowed more precise identification of the relevant allergens. In the past, they have been used to test for the occurrence of sensitization, and this may be cost-effective, but it leaves unclear which allergens are responsible for symptoms. 2, 3 Some test kits can identify a mixture of several allergens. In many places, mites, grass, and cat allergens are among the most common allergens, and most sensitized individuals can be identified by testing for relatively few allergens. Sensitization can be assessed directly by determining the presence of specific IgE to allergens in serum. Standardization is essential for this, and considerable effort has been made to provide standardized measures, particularly for international studies. Validity is essential to the measurement of absolute prevalence, but in many epidemiologic studies, we are as interested in relative prevalence, such as relative prevalence between age groups, countries, or districts, or differences between people exposed to various environmental or genetic risks. Although validity in an absolute sense may always be contested, what is as important in epidemiologic studies is standardization, meaning that the test is identical wherever and by whomever it is administered. Measuring the validity of a test for a condition that is poorly defined, such as asthma, is a problem because it presupposes a gold standard test with which the proposed test can be compared. Validity has two components: sensitivity, which is the ability of the test to identify an existing condition, and specificity, which is the ability to identify as normal people who are free of the condition. Validity implies that the result of the test coincides well with the true condition of the person being tested. 1 A test is reliable if it always gives the same answer when applied under similar circumstances. Good tests should possess reliability and validity.
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