Table 1.

Classification of chronic lower respiratory disease cases and severe chronic lower respiratory disease exacerbations

Classification	Criteria
CLRD case (subphenotypes*)
Probable	Physician documentation in the medical record of at least one of the following:
	• Past medical history or new diagnosis of COPD, emphysema, chronic bronchitis, and/or asthma (defines probable subphenotypes).
	• Outpatient prescription of inhaled long- or short-acting anticholinergic agent, inhaled corticosteroid (excluding intranasal administration), long-acting β-agonist, combination inhaled long-acting β-agonist and corticosteroid, theophylline, or roflumilast. Isolated inhaled short-acting β-agonist therapy does not qualify.
Highly probable	Confirmation of probable CLRD case, plus physician documentation of at least one of the following diagnostic test results, qualitatively or quantitatively, which may have been obtained during or before the current event:
	• Spirometry showing incompletely reversible airflow limitation (COPD).
	• Chest radiography or CT demonstrating emphysema (emphysema).
	• Spirometry or PEF showing reversible airflow limitation (asthma).
	• History of bronchitis event within the past 2 yr (chronic bronchitis)
Definite	Formal diagnostic test results from the current event in the medical record:
	• Spirometry with incompletely reversible airflow limitation, defined as post-bronchodilator FEV1/FVC ratio <0.70 or the LLN (COPD).
	• Chest radiography or CT demonstrating emphysema (emphysema), hyperinflation, or flattened diaphragm.
	• Spirometry showing reversible airflow limitation or PEF <70% predicted, with or without reversibility (defined by an observed improvement in PEF ≥30%), or, in the absence of repeated PEF, by a clear improvement in clinical status (if reversible and age of onset <45 yr, asthma).
	• Clinical history of bronchitis 3 mo/yr for the past 2 yr (chronic bronchitis).
CLRD exacerbation
Probable	Confirmation of probable CLRD case, combined with at least one of the following:
	• Self-report of new onset or worsening of dyspnea, cough, sputum, or wheeze.
	• Physical examination with use of accessory muscles, respiratory distress, wheezing, or prolonged expiration.
Highly probable	Confirmation of probable CLRD exacerbation, plus administration and/or prescription of systemic corticosteroids.
Definite	Confirmation of highly probable or definite CLRD case and highly probable CLRD exacerbation.

Definition of abbreviations: CLRD = chronic lower respiratory disease; COPD = chronic obstructive pulmonary disease; CT = computed tomography; LLN = lower limit of normal; PEF = peak expiratory flow.

^*Classification of CLRD subphenotypes was performed after establishment of whether and with what certainty CLRD was present. Subphenotype correspondence is indicated in brackets. Additional information is included in the online supplement.