Methods to assess RAST results in patients exposed to chemical allergens

RAST is routinely used to assess the presence of IgE antibodies against environmental allergens in the sera of symptomatic patients. With exposure to low-mol.-mass (chemical) allergens, RAST is also done, but the interpretation of results is more difficult. A study was undertaken to assess methods which have been employed to determine the positivity of sera and to develop an objective, statistically based procedure for determination of RAST positivity to chemical allergens. Sera were obtained from 14 nonsensitized (control) subjects and examined for total IgE by radioimmunoassay, and for cyanuric chloride (CyCl)-specific IgE by RAST. Linear regression analysis revealed the correlation between the tests to be 0.94. Equations for the 95% and 99% predicted intervals were obtained. Sera from 19 cyanuric chloride workers were tested for total and specific IgE. Positivity of RAST results was determined by three methods: RAST inhibition, RAST ratio (binding to CyCl-human serum albumin (HSA) disks/HSA disks), and the regression equation where values outside the 99% predicted interval were considered to be positive and those > 95% < 99% were considered to be borderline values. Determination of CyCl RAST positivity by the regression method gave results comparable to those obtained from RAST inhibition, whereas the RAST ratio resulted in many more false positive conclusions. This statistical approach to RAST analysis was also used to assess sera from patients exposed to the unrelated chemical allergens, toluene diisocyanate and formaldehyde. Conclusions based on the regression method were in good agreement with those from RAST inhibition assay. Moreover, use of one standard curve may be sufficient for interpretation of RAST results for diverse haptenic allergens. These results indicate that the regression method provides a statistical basis from which to determine positivity of RAST analyses while eliminating the need for RAST inhibition assays.