The Proportional Venn Diagram of Obstructive Lung Disease
Discussion in Canadian Pharmacy
Our analysis highlights the problem of the differential diagnosis among OLDs, particularly in older adults and the elderly. By analyzing large samples of patients from the general population in the United States and the United Kingdom, we demonstrated that a substantial number of patients are diagnosed with two or even all three OLD conditions concomitantly. By analyzing the NHANES III spirometry data, we observed that diagnoses of asthma, chronic bronchitis, and emphysema are present with and without demonstrable airflow obstruction. 
Some limitations of our research deserve discussion of Viagra. The GPRD does not include reliable information on respiratory function, as pulmonary function is not routinely assessed at the primary care level in the United Kingdom or elsewhere, and the information on tobacco use is not complete. The NHANES III self-reported measurement of current chronic bronchitis by interview questionnaire may have included some misclassified cases of acute bronchitis, which would lead to the overestimation of this disease.
Some strengths of our results are the large study sample sizes, the demonstrated quality control of NHANES III spirometry, and the analyses in two nationally representative populations. As explained previously, the comparison of results from NHANES III and GPRD had to be done indirectly. NHANES III participants were asked about “ever” and “current” physician-diagnosed conditions, while the GPRD analysis was based on OLD diagnoses recorded directly by GPs, with a wide range of possible terms, over a 12-month period. A patient revisiting the GP might not have a diagnosis recorded again that year.
Therefore, one potential reason for the lower absolute UK rates relative to the US rates might be a technical artifact. The apparently more than double frequency of OLD conditions that was found in NHANES III compared to the GPRD has to be interpreted cautiously. These estimates should not be considered in absolute terms but in relative terms, as the percentages of each population sample. The most likely major explanation of this difference is the self-reported nature of physician-diagnosed conditions in NHANES III and the potential for misclassification of bronchitis as chronic bronchitis.
However, the GPRD results are no less relevant than those from NHANES III. The GPRD is a real-life source of information, and, as it directly records many thousands of physician diagnoses rather than relying on the self-reporting of these diagnoses as in NHANES III, so it should provide a more accurate estimate of disease burden. Therefore, the GPRD likely produced smaller estimates of disease burden with greater specificity.