Amidolytic and immuno-nephelometric determination of alpha 1-proteinase inhibitor and alpha 2-macroglobulin in serum with calculation of specific inhibitor activities in health and disease.

Abstract

In sera of healthy persons (n = 50) and patients with a variety of diseases (n = 197) the two major proteinase inhibitors, alpha 1-proteinase inhibitor (alpha 1-antitrypsin) and alpha 2-macroglobulin, were measured by two methods: a chromogenic (amidolytic) substrate assay to assess the functional activities, and a laser nephelometric method to determine the immunoreactive concentrations of the respective proteins. The specific proteinase inhibitor activities defined as the number of inhibitor units per g inhibitor protein were calculated. The precision and accuracy of both assays were found to be similar, showing a satisfactory correlation of results for the sera of healthy persons (r = 0.916 for alpha 2-macroglobulin and 0.988 for alpha 1-proteinase inhibitor). In diseased individuals the correlation was lower than in normal persons (0.862 for alpha 2-macroglobulin and 0.907 for alpha 1-proteinase inhibitor). A poor correlation was obtained in patients with liver diseases (r = 0.586 for alpha 1-proteinase inhibitor and 0.852 for alpha 2-macroglobulin). Reference ranges were established for functional and immunological concentrations and for specific inhibitor activities, respectively. Normal values followed a Gaussian distribution. In patients with various diseases including those with acute phase response, the specific inhibitor activities of alpha 1-proteinase inhibitor are reduced significantly; this is because inhibitor activity shows a smaller relative increase than immunoreactivity. Among the various diseases, no significant differences were noted. The specific inhibitor activity of alpha 2-macroglobulin changed significantly only in patients with carcinoma, liver diseases and trauma. Follow up of some patients shows also intraindividual variation of specific proteinase inhibitor activities.