Amidolytic and Immuno-Nephelometric Determination of α1-Proteinase Inhibitor and α2-Macroglobulin in Serum with Calculation of Specific Inhibitor Activities in Health and Disease

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Abstract
In sera of healthy persons (n = 50) and patients with a variety of diseases (n = 197) the 2 major proteinase inhibitors, .alpha.1-proteinase inhibitor (.alpha.1-antitrypsin) and .alpha.-macroglobulin, were measured by 2 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 were 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.