RAPID SCREENING ASSAY FOR ANTI-GBM ANTIBODY AND ANCAS - AN IMPORTANT TOOL FOR THE DIFFERENTIAL-DIAGNOSIS OF PULMONARY RENAL SYNDROMES

Background. Pulmonary renal syndrome is encountered in several disease s such as Goodpasture's syndrome, antineutrophil cytoplasmic antibody (ANCA) associated systemic vasculitis, systemic lupus erythematosus (S LE) and infection-associated or drug-induced glomerulonephritis. To pr eserve organ function it is of vital importance to make the correct di agnosis and institute adequate therapy early, in the acute phase. Meth od. An enzyme-linked immunosorbent assay (ELISA), specially designed a s a rapid screening assay for antiglomerular basement membrane (anti-G EM) antibody, proteinase-3 (PR3-) ANCA and myeloperoxidase-(MPO-) ANCA were evaluated from 1060 serum samples drawn from patients with clini cally suspected pulmonary renal syndrome or rapidly progressive glomer ulonephritis (RPGN). Results. Of the 1060 serum samples, 142 were posi tive for anti-GEM antibody (n=19), PR3-ANCA (n=60), or MPO-ANCA (n=73) . Of the 142 samples, IO were double positive. Reanalysis of positive sera with a quantitative ELISA yielded results manifesting good correl ation with those of the the rapid screening assay. Of 918 sera found t o be negative in the rapid screening assay, 105 were also tested with IIF, 11 being found to be positive. However, these 11 sera manifested no specificity for PR3 or MPO, but some were specific for bactericidal /permeability-increasing proteins, lactoferrin or elastase ANCAs. Two of the patients whose sera yielded negative results in the rapid assay had systemic vasculitis. Conclusion. The ELISA thus detects the true antibodies to PR3, MPO, and GEM, whereas IIF detects additional specif icities. The findings suggest the rapid assay results to be of high po sitive predictive value, and the assay to be of high diagnostic specif icity and sensitivity and thus useful in the diagnostic workup in susp ected cases of RPGN or pulmonary renal syndrome.