Eleven studies (n=31,333, sample size range 63 to 11,676) were included in the review: seven cross-sectional studies (n=19,243); and four retrospective studies (n=12,090). The quality scores ranged from 8 to 11. There was no evidence of publication bias.
Pooled results showed that the FEV1/FEV6 was an acceptable surrogate for FEV1/FVC. Sensitivity was 0.89 (95% CI 0.83 to 0.93) and specificity was 0.98 (95% CI 0.95 to 0.99). Positive likelihood ratio was 45.46 (95% CI 18.26 to 113.21) and negative likelihood ratio was 0.11 (95% CI 0.08 to 0.17). Diagnostic odds ratio was 396.02 (95% CI 167.32 to 937.31) and the diagnostic score was 5.98 (95% CI 5.12 to 6.84). The SROC curve showed a high level of overall accuracy, with an area under the curve of 0.97 (95% CI 0.95 to 0.98; Q* point: 0.95). There was no evidence of a threshold effect, but there was statistically significant heterogeneity between the studies (p<0.001).
Multiple regression analysis showed that prevalence of airway obstruction had a statistically significant effect on diagnostic odds ratio (relative DOR 1.12, 95% CI 1.00 to 1.25, p=0.05). There was no statistically significant effect in terms of choice of cut-off point.