Determination of human granulocyte elastase by the immunoactivation method on the Hitachi 717 automated analyser

This paper describes a fully mechanized homogeneous immunoassay using the immunoactivation method for the rapid and specific determination of human granulocyte elastase (EC 3.4.21.37) in plasma. The method uses anti-elastase antibody fragments from sheep, conjugated to horseradish peroxidase. These enzyme-antibody conjugates bind to the elastase-alpha 1-proteinase inhibitor complex present in plasma. A separate sample blank with non-specific sheep antibody fragments conjugated to horseradish peroxidase corrects for errors introduced by the sample matrix. Measurements were performed with the clinical chemistry analyser Hitachi 717. A single determination can be performed in 10 min, requiring 24 microliters sample volume. The measuring range is about 20 to 1000 micrograms/l elastase. For within-run precision the coefficients of variation are 4.77%, 4.48% and 1.85% for elastase concentrations of 45.7, 89.1 and 385.4 micrograms/l; for day-to-day precision the coefficients of variation are 15.81%, 7.19% and 4.12% for elastase concentrations of 31.1, 65.5 and 440.2 micrograms/l, respectively. Correlation (y = bx + a) of results with those from the heterogeneous immunoassay showed a good agreement (r = 0.93, b = 1.11, a = -27.0, N = 121). Interferences by endogeneous substances and by drugs at therapeutic doses were not observed. The reference interval, determined by using plasma from 215 healthy individuals (C-reactive protein less than 5 mg/l, leukocyte count 4-8 x 10(9)/l), was 9-56 micrograms/l (2.5th to 97.5th percentile), with a median of 27 micrograms/l.