This study sought to determine the prevalence of airway obstruction in smokers in a primary care setting using the LFQ as a case-finding tool and confirming the diagnosis with spirometry. Previous epidemiological studies of COPD prevalence either have been non–clinic-based4
or have used ambulatory care claims data. This cross-sectional survey of ambulatory clinics is representative of what primary care physicians are likely to see in their offices.
In the primary care offices studied, obstructive airway disease was not uncommon in any age group screened, even in those younger than 50 years, who are rarely assessed for COPD in primary care. The LFQ retained high sensitivity and negative predictive value, important characteristics for case-finding purposes.
A simple, cost-effective strategy to identify a large group of patients with undiagnosed symptomatic obstructive lung disease is needed to address this important public health concern. Most primary care physicians do not have office spirometry equipment and thus do not have ready access to an objective test necessary for both diagnosis and management of COPD. The LFQ may be adopted as a method to identify patients at risk of obstructive lung disease. An LFQ score of 18 or less might encourage primary care physicians to refer patients for spirometry. Given its high negative predictive value, the LFQ also has the potential to decrease the use of spirometry in asymptomatic patients and guide other diagnostic evaluations in symptomatic patients with spirometric evidence of obstructive lung disease.22,23
Although our primary aim in the development of the LFQ was to identify patients who were candidates for further assessment using spirometry (and potentially to identify undiagnosed cases of COPD), a substantial number of abnormal spirometry measures (eg, FEV1 <80% of predicted) were also identified using the LFQ. We based our a priori criteria for the success of the LFQ on its ability to detect airway obstruction, but its clinical utility may actually be much greater because of its potential also to detect clinically important restrictive diseases.
The National Lung Health Education Program previously recommended screening spirometry for all current or former smokers aged 40 years or older to identify undiagnosed COPD.24
However, on the basis of the results of the Agency for Heathcare Research and Quality evidence report and the recommendations of the US Preventive Services Task Force, most organizations no longer recommend this approach of universal screening.23
We found that 762 (95%) of 800 patients recruited from a primary care setting who were not taking any respiratory medications, who scored 18 or less on the LFQ, and who had an FEV1
/FVC ratio of less than 0.70 did not report a previous diagnosis of COPD. Thus, the LFQ, as a preliminary case-finding tool, may be an acceptable alternative to mass screening.
The estimated COPD prevalence of 17.9% in primary care practice is much higher than the 3.0% to 5.0% prevalence in the general population.6
This finding may not be entirely unexpected because people visiting primary care physicians are a population generally more inclined to seek care for signs, symptoms, and previously recognized diseases. The practice-based prevalence will of course vary by age and smoking prevalence in this population.
This study has limitations. Selection bias is a potential limitation that could lead to an overestimation or underestimation of prevalence if outcomes of interest are significantly different in study patients vs the general population. To limit selection bias at the initial recruitment stage, sites were trained to use standardized recruitment protocols to screen and recruit eligible patients. Further, spirometry was performed only on a subset of patients. It should also be noted that the assessment of screening accuracy in the current study was limited because only a small subset scoring more than 18 on the LFQ completed spirometry. This study population may not be representative of the entire primary care population.