Pulmonary function tests · Interpreting the nonspecific pattern
The nonspecific pulmonary function test pattern: longitudinal follow-up and outcomes
| Design | Retrospective longitudinal cohort study |
|---|---|
| Treatment | Serial pulmonary function testing in patients showing the nonspecific pattern |
| Control | Comparison with restrictive and obstructive patterns on follow-up |
| Population | 1284 subjects contributing 3674 pulmonary function tests |
| Follow-up | Median 3 years |
| Primary endpoint | Stability of the nonspecific pattern on repeat testing |
| Result | At last follow-up 818 of 1284 (64%) still showed the nonspecific pattern, 208 (16%) a restrictive pattern, 191 (15%) an obstructive pattern and 42 (3%) another pattern. |
| Secondary endpoints | Diagnoses associated with the pattern, clinical outcomes |
The NS pattern is a distinct and stable PF test pattern with roughly two-thirds of patients continuing to show this pattern on follow-up testing. Current interpretation guidelines erroneously label the NS pattern as representing obstruction and need to be changed to reflect these data.
The trial authors, in the published abstract
A study that told the guidelines they were wrong, with data rather than opinion. The nonspecific pattern is a normal total lung capacity and a normal FEV1/FVC ratio with a low FEV1, a low FVC or both — not restriction, and not early obstruction. Useful at the bedside when a report suggests obstruction on a pattern that will still look the same in three years.
Iyer VN, Schroeder DR, Parker KO, et al. The nonspecific pulmonary function test: longitudinal follow-up and outcomes. Chest 2011 Apr;139(4):878-886.