Risk levels for mite allergen: are they meaningful, where should samples be collected, and how should they be analyzed?

Indoor allergen exposure plays a major role in the development of sensitiza tion and triggering of asthma in children. All over the world, mites are co mmon sources of indoor allergens. Risk levels for mite-allergen exposure ha ve been recommended. A mite-allergen level of greater than or equal to 2 mu g/g dust is considered a risk level for sensitization and symptoms of asth ma. Data from several ongoing prospective studies of children show that mit e sensitization may occur below the suggested threshold level. However, fro m these studies, it seems that high mite-allergen exposure increases the ri sk of early sensitization, whereas low exposure levels probably take a long er time to induce sensitization. Assessment of allergen exposure and consid eration of allergen-elimination strategies should not be limited only to th e home environment. High levels of mite allergens are also found in day-car e centers, schools, and various other public places, such as bars. Thus, in addition to homes, these environments should also be considered when aller gen-avoidance measures are taken. Allergen content in dust can be expressed in several units, e.g., ng/g, ng/m(2), and ng/sampling, and as the total a mount of allergen. At present, there is no consensus on the best way to mea sure and express mite-allergen levels. In this paper, aspects of threshold levels for mite sensitization, various exposure environments, and sampling, determination, and expression units of mite exposure will be discussed in brief.