Measurement of plasma concentrations of polymorphonuclear elastase-alpha 1 proteinase inhibitor (elastase-alpha 1 antitrypsin) in patients with rheumatoid arthritis: interference by rheumatoid factor.

The plasma concentration of granulocyte elastase in complex with alpha 1 proteinase inhibitor was determined in 32 patients with rheumatoid arthritis and eight with seronegative spondarthritis complicated by peripheral joint synovitis. Most patients had concentrations of complex which were within the range of the control group when measured by an 'in-house' enzyme linked immunosorbent assay, though several of the patients with rheumatoid arthritis had raised concentrations. When the complexes were measured by a commercially available assay, however, much higher values were obtained for many of the patients with rheumatoid arthritis. Evidence is presented indicating that the commercially available assay may suffer seriously from interference by rheumatoid factor. The possibility is discussed that most patients with rheumatoid arthritis may have plasma concentrations of elastase-alpha 1 PI which are normal or only slightly raised, and that previously published reports using assay systems similar to that available commercially might also have produced falsely raised values for many individuals with rheumatoid arthritis.