COPD and asthma: Diagnostic accuracy requires spirometry

Barriers to the use of spirometry in the primary care setting exist on several levels. Providers may lack knowledge of clinical practice guidelines that recommend spirometry in the diagnosis of COPD, and they may lack general awareness of the utility of spirometry.^25-29 In 2 studies of primary care practices that offered office spirometry, lack of knowledge in conducting and interpreting the test was a barrier to its use.^28,30 Primary care physicians also struggle with logistical challenges when clinical visits last just 10 to 15 minutes for patients with multiple comorbidities,²⁷ and maintenance of an office spirometry program may not always be feasible.

Getting to the right diagnosis

Guideline-based treatment recommendations differ for COPD and asthma, and mistakenly treating the wrong condition can lead to adverse events (AEs). For instance, while inhaled corticosteroids use is common in patients with persistent asthma, its use in COPD increases the risk of pneumonia³¹ and thus is usually reserved for add-on treatment mainly if patients experience continued exacerbations. Use of long-acting beta-agonists (LABAs) as monotherapy is appropriate in COPD but not so in the management of asthma. In 2006, a large randomized controlled trial evaluated a LABA (salmeterol) vs placebo added to usual care and found more serious AEs and asthma-related deaths in the salmeterol group.^32,33 Thus LABA monotherapy is not recommended in asthma guidelines.

Likewise, nonpharmacologic interventions may be misused or go unused when needed if the diagnosis is inaccurate. For patients with COPD, outcomes are improved with pulmonary rehabilitation and supplemental oxygen in the setting of resting hypoxemia, but these resources will not be considered if patients are misdiagnosed as having asthma. A patient with undetected heart failure or obstructive sleep apnea who has been misdiagnosed with COPD or asthma may not receive appropriate diagnostic testing or treatment until asthma or COPD has been ruled out with lung function testing.

Objectively documenting the right diagnosis helps ensure guideline-based management of COPD or asthma. Ruling out these 2 disorders prompts further investigation into other conditions (eg, coronary artery disease, heart failure, gastroesophageal reflux disease, pulmonary hypertension, interstitial lung diseases) that can cause symptoms such as shortness of breath, wheezing, or cough.

The TABLE^2,10,34 summarizes some of the more common clinical and spirometric features of COPD and asthma. Onset of COPD usually occurs in those over age 40. Asthma can present in younger individuals, including children. Tobacco use or exposure to noxious substances is more often associated with COPD. Patients with asthma are more likely to have atopy. Symptoms in COPD usually progress with increasing activity or exertion. Symptoms in asthma may vary with certain activities, such as exercise, and with various triggers. These features represent “typical” cases of COPD or asthma, but some patients may have clinical characteristics that do not fit easily into one disease pattern, making diagnostic testing of lung function even more essential.

Continue to: The utility of spirometry in measuring lung function