Mite allergens. Collection, determination, expression of results, and risk levels for sensitization and symptom induction.

The presence of mite allergens in dust can be determined by counting mites at different stages of development in dust and by determination of the major allergen content (Der p 1 ) in dust and air, which is crucially important to allergic patients. For comparison of results, similar methods for collection of dust and air must be used. Due to their size, mite bodies and fecal particles are airborne only directly after disturbance. Special filters should be used for dust collection, and upholstered surfaces should be vacuumed for 2 min/m2 (minimum 4 m2) and hard surfaces for 1 min/m2 (minimum 8 m2). Heavy contaminations should be removed. Preferably, the method given in the ISAAC study should be followed. Samples should be deep-frozen for at least some days to kill the mites. ELISA techniques, preferably using polyclonal antibodies and antigen with all isoforms present, should be used for determination of allergens. The allergen load has been given in ng/g of dust, but allergen/m2 or per sample area should be preferred. Allergen in the air should be given in pg/m3. A tentative limit of 2000 ng/g was proposed for sensitization and asthma. This limit is still valid on a population basis, but recent data indicate that highly susceptible young children become sensitized at concentrations 10-100 times lower and that ng levels of cat allergen/m3, as found in schools, induce chronic asthma.