Spirometry (FEV1/FVC < 0.70) — COPD

Test Characteristics

Metric	Value
False-negative rate	8% (sensitivity 92%)
False-positive rate	16% (specificity 84%)
Bayes factor (positive test)	5×
Bayes factor (negative test)	1/10×
Base rate	5% of US adults

Interpreting Results

Scenario	Prior	+ Result	− Result
Unselected adult	5%	5 × 5% = 25%5%× 525%	1/10 × 5% = 0.5%5%÷ 100.5%
Current smoker with chronic dyspnea	20%	5 × 20% ≥ 100%20%× 5100%	1/10 × 20% = 2%20%÷ 102%

5 × 20% ≥ 100%20%× 5100%: exact posterior is 56%. Fixed FEV1/FVC threshold of 0.70 overdiagnoses COPD in older adults and underdiagnoses in younger patients.

• + result: risk goes from vegetarian (5%) to face card from a deck (25%)
• − result: risk drops to identical twin (0.5%)

Sources:

• AAFP. Office spirometry.
• BMC Pulmonary Medicine, 2009. Spirometry in primary care.

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