Precipitins in bird breeder's disease: how useful are they?

Precipitating antibodies to avian antigens play a controversial role in the diagnosis of bird breeder's disease (BBD). In order to establish the sensitivity, specificity and accuracy of precipitins in our laboratory, we conducted a prospective study including 128 sera received in 1988 for determination, by immunoelectrophoresis, of avian precipitins. Accurate information was obtained for 90 patients; definitive clinical diagnosis was given by the patient's own physician. We found a high sensitivity (86%), specificity (93%) and accuracy (92%) of avian precipitins in the diagnosis of BBD. Bayes' theorem was applied to determine the predictive value of the test with varying disease prevalence, and established that precipitins were particularly valuable for low or medium a priori probability. Using the receiver operating characteristic (ROC) curve we evaluated the effects of varying the positivity threshold of precipitins. The threshold used in this study appeared to offer the best compromise between sensitivity and specificity. These results suggest that the diagnostic value of avian precipitins in the work-up of BBD should be reconsidered, also because they represent a simple, cheap and non-invasive diagnostic test.