COPD: Multiple Measures Needed to Avoid Overdiagnosis

Clinicians should rely on both a low forced expiratory volume in 1 second (FEV₁)/forced vital capacity (FVC) (according to fixed ratio and/or lower limit of normal [LLN]) and a low FEV₁ to avoid misdiagnosing chronic obstructive pulmonary disease (COPD), according to a cross-sectional study.

Wouter van Dijk, MD, PhD, from the Department of Primary and Community Care, Radboud University, Nijmegen Medical Centre, the Netherlands, and the Respiratory Epidemiology and Clinical Research Unit, Montreal Chest Institute, McGill University, Quebec, Canada, and colleagues report their findings in an article published in the January/February issue of the Annals of Family Medicine.

Up to 25% of people aged 40 years and older are thought to have COPD. However, prevalence estimates in previous studies appear to depend on which diagnostic test is used, and few studies have tested the accuracy of current diagnostic criteria in the context of patient outcomes. Taken together, Dr van Dijk and colleagues suggest that overdiagnosis or underdiagnosis may be common. Because diagnosis can lead to use of medicines to reduce symptoms, the research team adds that "overdiagnosis rather than underdiagnosis is a more pressing issue in clinical practice."

Debate continues about which of two measures best provides spirometric evidence of airflow limitation to diagnose COPD. One camp favors a ratio of FEV₁ to FVC of less than 0.7 alone or in tandem with low FEV₁, at less than 80% of predicted value. Others endorse a FEV₁/FVC ratio below the fifth percentile, also known as the LLN.

To determine which measure is better at identifying clinically significant disease, the research team evaluated data from 4882 people aged 40 years and older enrolled in the Canadian Cohort of Obstructive Lung Disease (CanCOLD) study. Data for the longitudinal cross-sectional study were collected between August 2005 and May 2009. The mean age of the patients included in the study was 57 years, and 43% were men. The group's mean FEV₁ was 95.0% of normal.

Based on fixed ratio criteria, 17% of the study population had spirometric airflow limitation compared with 11% based on LLN. All but 0.3% of the patients diagnosed by LLN were also diagnosed with fixed ratio.

When the researchers compared adverse outcomes, such as respiratory symptoms, disability, health status, exacerbations, and cardiovascular disease, within each diagnostic group, they found that patients diagnosed with both fixed ratio and LLN were sicker than those diagnosed with fixed ratio only.

Specifically, after adjustments for age, sex, and ever smoking, patients who met both the fixed ratio and LLN criteria were at increased risk for wheeze (odds ratio [OR], 3.25; 95% confidence interval [CI], 2.65 - 3.97), chronic bronchitis (OR, 3.14; 95% CI, 2.25 - 4.37), and chronic phlegm (OR, 3.04; 95% CI, 2.39 - 3.87) and had an OR of 2.33 (95% CI, 1.92 - 2.82) for disability by the Medical Research Council dyspnea scale when compared with peers who met neither criterion for airflow limitation.

In contrast, those diagnosed via fixed ratio alone were at elevated risk for physician-diagnosed wheeze (OR, 1.54) and cardiovascular disease (OR, 1.52), but not for other outcomes.

However, the researchers saw the highest risk for poor outcomes among those participants diagnosed using low FEV₁ with either fixed ratio or LLN (or both). Among those patients, the odds ratios increased to 4.58 (95% CI, 3.51 - 5.96) for wheeze, 4.48 (95% CI, 3.09 - 6.51) for chronic bronchitis, 4.10 (95% CI, 3.08 - 5.46) for chronic phlegm, and 3.86 (95% CI, 3.03 - 4.92) for the Medical Research Council dyspnea scale.

Patients with moderate to severe airflow limitation, as evidenced by low FEV₁ with either fixed ratio or LLN (or both), also had significantly elevated risk for cardiovascular disease (OR, 1.51 - 1.56).

"[T]he results indicated that overdiagnosis could be a problem when using a single criterion, either fixed ratio or LLN, as patients with overdiagnosis, having a normal FEV₁, (one of at least 80% of predicted), appear to experience few patient reported outcomes; that is, they do not appear to have clinically relevant disease," the authors write.

"Our results indicated that a low FEV₁/FVC ratio by either the fixed ratio or LLN criterion coupled with a low FEV₁ (<80% of predicted) is the most clinically relevant diagnostic criterion for COPD," they conclude.

Financial support for the study was provided by the Canadian Institute of Heath Research Collaborative Research Program, which includes AstraZeneca Canada Ltd, Boehringer-Ingelheim Canada Ltd, GlaxoSmithKline Canada Ltd, Merck, Novartis Pharma Canada Inc, Nycomed Canada Inc, and Pfizer Canada Ltd as industry partners; the Respiratory Health Network of the Fonds de recherche du Québec; and the Research Institute of the McGill University Health Centre.

Ann Fam Med. 2015;13:41-48. Full text

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Cite this: COPD: Multiple Measures Needed to Avoid Overdiagnosis - Medscape - Jan 27, 2015.