Spirometry: Thinking Beyond the COPD “Gold Standard”

Spirometry is considered the gold standard for confirming the diagnosis of chronic obstructive pulmonary disease (COPD) and assessing treatment response.¹ Studies find that using it can improve the care provided and overall outcomes of COPD patients in primary care settings.^2-6

Given all this emphasis on spirometry, you might think that it is impossible to diagnose and treat COPD without using it. Yet numerous studies find that primary care physicians underuse spirometry with their COPD patients.^7-11 Are they providing substandard care?

Not necessarily. A new review of the evidence for lung function tests, published in Current Opinions in Pulmonary Medicine, contends that despite the benefits of spirometry, it is just one element of correct COPD diagnosis.¹²

The paper’s findings fit perfectly with a major change in the most recent GOLD guidelines: Namely, that spirometry should be used to make a “confident diagnosis” of COPD, not to “support a diagnosis,” as the old guidelines recommended.¹ What does this mean? The 2011 guidelines call for diagnosing COPD on the basis of symptom severity, future risk of exacerbations, and identification of comorbidities, in addition to the severity of abnormalities found with spirometry.

The new review article, from pulmonologists at the University of Hong Kong, lists several reasons for decreasing reliance on spirometry alone for COPD diagnosis.

First, different guidelines have different criteria for airflow obstruction. For instance, GOLD and the American Thoracic Society/European Respiratory Society guidelines define it as an FEV₁/FVC of 0.7 or less, while the National Institute for Health and Clinical Excellence (NICE) defines it as an FEV₁/FVC lower than 0.7. Using these different definitions in a single study resulted in a diagnosis range of 7.4% to 34.1% within a single cohort.¹³

In addition, age and sex can bias the results of spirometry, since they affect “normal” lung function. Spirometry measures decline with age, which could lead to a higher diagnosis in the elderly. Thus, the GOLD guidelines suggest a lower fixed ratio of 70% for elderly patients. There is also some movement away from fixed percentages of lung function to the lower limit of normal (LLN), with Spanish and Latin American COPD guidelines defining airflow obstruction as below the LLN for someone aged 61 or older.

In a recent study of 11,413 patients, using a fixed ratio of 70% for FEV₁/FVC and 80% of predicted for other indicators misdiagnosed and misclassified up to one-fifth of patients, when compared with the accepted limit of normality in the LLN.¹⁴ Using an indicator of FEV₁/FVC below LLN, rather than fixing it at 70%, could improve diagnosis.¹⁵

However, neither the fixed ratio nor the LLN is ideal for diagnosis, note the authors of the review article, because their reference values are based on a “healthy general population” with no consideration of smoking status, genetic predisposition for COPD, or exposure to air pollution or particulates shown to cause the disease. The use of either should be localized to the population within a specific geographic area, they caution.

However, the FEV₁ does appear to be predictive of lung function decline and exacerbation frequency, the authors write, and it also appears to correlate well with at least one genetic polymorphism associated with COPD.

So what’s a primary care physician to do? If you don’t feel comfortable diagnosing and managing COPD in your patients on the basis of spirometry and clinical parameters, it may be time for a referral to a pulmonologist. A specialist may be able to use other tests, such as expiratory flow limitation at rest (EFLT), to confirm diagnosis and assess lung function.

The authors also urge clinicians to adopt a validated questionnaire to assess their patient’s disease state. The most recent GOLD guideline update reflects this, suggesting that you incorporate symptom assessment tools into decisions about treatment. Specifically, the guidelines recommend using the COPD Assessment Test (CAT) and/or the Modified British Medical Research Council (mMRC) questionnaire every 2 to 3 months to identify “trends and changes,” rather than relying only on annual spirometry to assess symptoms.

The guidelines also recommend asking the following questions when evaluating treatment efficacy:

• Have you noticed a difference since starting this treatment?
• If you are better:
    – Are you less breathless?
    – Can you do more?
    – Can you sleep better?
    – Describe what difference it has made to you. Is that change worthwhile to you?

In the end, the review article highlights 3 important points for all clinicians who diagnose and treat COPD:

1. Forget about population-based screening with current spirometric definitions.
2. Use lung function tests to diagnose airflow obstruction that is not fully reversible and classify COPD severity.
3. Consider clinical respiratory symptoms-not just the results of lung function tests-when diagnosing and managing the disease.

 

References:

REFERENCES:
1. From the Global Strategy for the Diagnosis, Management and Prevention of COPD, Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2011. Available from: http://www.goldcopd.org/.

2. Walker PP, Mitchell P, Diamantea F, et al. Effect of primary-care spirometry on the diagnosis and management of COPD. Eur Respir J. 2006;28:945–952.

3. Poels PJ, Schermer TR, van Weel C, et al. Spirometry in chronic obstructive pulmonary disease. BMJ. 2006;333:870–871.

4. Dales RE, Vandemheen KL, Clinch J, Aaron SD. Spirometry in the primary care setting: influence on clinical diagnosis and management of airflow obstruction. Chest. 2005;128:2443–2447.

5. Bolton CE, Ionescu AA, Edwards PH, et al. Attaining a correct diagnosis of COPD in general practice. Respir Med. 2005;99:493–500.

6. Chavannes N, Schermer T, Akkermans R, et al. Impact of spirometry on GPs’ diagnostic differentiation and decision making. Respir Med. 2004;98:1124–1130.

7. Damarla M, Celli BR, Mullerova HX, Pinto-Plato VM. Discrepancy in the use of confirmatory tests in patients hospitalized with the diagnosis of chronic obstructive pulmonary disease or congestive heart failure. Respir Care. 2006;51:1120–1124.

8. Mapel DW, Hurley JS, Frost FJ, Petersen HV. Health care utilization in chronic obstructive pulmonary disease. A case-control study in a health maintenance organization. Arch Intern Med. 2000;160:2653–2658.

9. Lee TA, Bartle B, Weiss KB. Spirometry use in clinical practice following diagnosis of COPD. Chest. 2006;129:1509–1515.

10. Anthonisen NR, Woodlrage K, Manfreda J. Use of spirometry and respiratory drugs in Manitobans over 35 years of age with obstructive lung diseases. Can Respir J. 2005;12:69–74.

11. Walker P, Mitchell P, Diamantea F, Warburton C, Davies L. Effect of primary-care spirometry on the diagnosis and management of COPD. Eur Respir J. 2006;28:945–952.

12. Lam DCL, Hui CKM, Ip MSM. Issues in pulmonary function testing for the screening and diagnosis of chronic obstructive pulmonary disease. Curr Opin Pulm Med. 2012;18:104–111.

13. Lindberg A, Jonsson AC, Ronmark E, et al. Prevalence of chronic obstructive pulmonary disease according to BTS, ERS, GOLD and ATS criteria in relation to doctor’s diagnosis, symptoms, age, gender, and smoking habits. Respiration. 2005;72:471–479.

14. Miller MR, Quanjer PH, Swanney MP, et al. Interpreting lung function data using 80% predicted and fixed thresholds misclassifies more than 20% of patients. Chest 2011;139:52–59.

15. Hwang YI, Kim CH, Kang HR, et al. Comparison of the prevalence of chronic obstructive pulmonary disease diagnosed by lower limit of normal and fixed ratio criteria. J Korean Med Sci. 2009;24:621–626.

16. Casanova C, de Torres JP, Aguirre-Jaime A, et al. The progression of chronic obstructive pulmonary disease is heterogeneous: the experience of the BODE cohort. Am J Respir Crit Care Med. 2011;184:1015–1021.