The quantitation of antibody in farmer's lung syndrome using a radioimmunoassay. Results of a clinical survey and comparison of three serological methods.

Three serological tests for antibody to Micropolyspora faeni, the precipitin test (Ouchterlony double diffusion test in two dimensions) the fluorescent antibody test (double-layer technique using patient's serum in middle layer) and a quantitative radioimmunoassay for IgG antibody were applied to cases of farmer's lung syndrome and compared as to their value in diagnosis and management of these cases. Of twenty-one cases with clinical symptoms only ten (48%) had positive precipitin tests, while all (100%) showed a positive fluorescent antibody test. Sixteen (76-4%) were found by the radioimmunoassay to have antibody in excess of the normal controls. The remaining five cases with symptoms had a range of antibody levels which overlapped with those of symptom-free individuals (with sera negative to fluorescent antibody tests). The precipitin test was positive above a level of 75 mug/ml of IgG antibody as determined by the radioimmunoassay, whilst the cases judged by the fluorescent antibody test to be positive were all above a level of 35 mug/ml of IgG antibody. Application of the radioimmunoassay to a group of farmers in the West of Scotland successfully detected high antibody levels in all with clinical evidence of farmer's lung syndrome; farmers who were symptom-free also had measurable antibody. The advantages of a quantitative test for antibody levels in the management of cases of this disease are discussed.