Assessment of comorbidities and prognosis in patients with COPD diagnosed with the fixed ratio and the lower limit of normal: a systematic review and meta-analysis.

The patients with airflow limitations according to FR were more likely to exacerbate than those with LLN only. Patients that met either FR or LLN were more likely to have higher mortality than FR-/LLN-. There was no difference between the FR+/LLN- and FR-/LLN+ groups for the occurrence of comorbidities.