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 sensitization and triggering of asthma in children. All over the world, mites are common sources of indoor allergens. Risk levels for mite-allergen exposure have been recommended. A mite-allergen level of >/=2 microg/g dust is considered a risk level for sensitization and symptoms of asthma. Data from several ongoing prospective studies of children show that mite sensitization may occur below the suggested threshold level. However, from these studies, it seems that high mite-allergen exposure increases the risk of early sensitization, whereas low exposure levels probably take a longer time to induce sensitization. Assessment of allergen exposure and consideration of allergen-elimination strategies should not be limited only to the home environment. High levels of mite allergens are also found in day-care centers, schools, and various other public places, such as bars. Thus, in addition to homes, these environments should also be considered when allergen-avoidance measures are taken. Allergen content in dust can be expressed in several units, e.g., ng/g, ng/m2, and ng/sampling, and as the total amount of allergen. At present, there is no consensus on the best way to measure 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.