Five studies were included (n=1,509 patients): one randomised controlled trial (n=56 patients); three parallel-group comparative studies (n=1,357 patients); and one pre-test/post-test study (n=96 patients). Data collection was at least partially prospective in all five studies. The single RCT was double-blind, but the method of allocation concealment was unclear. Publication bias was not present in the analysis, but there was evidence of statistical heterogeneity (p=0.012) for the main analysis.
Overall, augmentation with alpha1-antitrypsin was associated with a slower decline in the forced expiratory volume in one second (FEV1) slope than control groups (slope difference 13.4mL/year, 95% CI 1.5 to 25.3; five studies).
Augmentation was most effective in patients with a baseline FEV1 of 30 to 65% (slope difference 17.9mL/year, 95% CI 9.6 to 26.1; four studies).
In patients with a baseline FEV1 of less than 30% (four studies) or greater than 65% (three studies), there was no statistically significant benefit of augmentation compared with control groups.
Sensitivity analysis indicated that the results were generally robust.