SPECIFIC IGE TO ISOCYANATES - A USEFUL DIAGNOSTIC ROLE IN OCCUPATIONAL ASTHMA

Background: Isocyanates are the most frequent cause of occupational as thma in industrialized countries. Objective: We sought to investigate the utility of specific IgE measurement in the diagnosis of isocyanate -induced asthma. Methods: Fifty-eight of 101 patients referred for inv estigation were diagnosed as having isocyanate-induced occupational as thma by means of history, serial peak flow records, and bronchial prov ocation tests. Specific IgE antibodies to toluene diisocyanate:human s erum albumin (HSA), diphenylmethane diisocyanate:HSA, and hexamethylen e diisocyanate: HSA were measured in all patients by Phadebas RAST. Re sults: Twenty patients had a RAST ratio of 2 or greater to at least on e isocyanate. Thirteen (28%) of the 46 patients with a positive provoc ation test response had a RAST ratio of 2 or greater, and nine (20%) h ad a RAST ratio of 3 or greater. Raising the RAST cut-off from 2 or gr eater to 3 or greater reduced its sensitivity but increased the specif icity of the test to 100%. RAST measurement was most likely to be posi tive within 30 days of exposure. Serial measurements suggested that th e half-life of the IgE antibodies was approximately 6 months. Evidence of cross-reactivity between isocyanate RAST responses was found in ei ght subjects. Conclusion: Specific IgE to isocyanates is a more specif ic than sensitive index of occupational asthma. With a RAST score of 3 or greater, it is wholly specific and therefore diagnostic of isocyan ate-induced asthma. The sensitivity of specific IgE measurement is hig hest when blood is taken less than 30 days from last exposure, which i s consistent with the observed half-life.