Table 4.

Diagnostic values of smoking habit, respiratory symptoms, and chest signs in predicting severe COPD (postbronchodilator FEV₁/FVC < 0.7 and FEV₁% predicted <50) in 375 patients diagnosed with asthma or COPD

	Sensitivity	Specificity	LR	CI	PPV (%)
Smoking
>0 pack-years	0.96	0.28	1.3	1.2–1.5	15.1
≥20 pack-years	0.72	0.65	2.1	1.6–2.7	22.3
≥40 pack-years	0.30	0.92	3.9	2.2–7.1	35.1
Respiratory symptoms during the previous week
Short of breath at rest, several times or more	0.23	0.91	2.4	1.3–4.6	24.4
Short of breath doing physical activities, several times or more	0.89	0.54	1.9	1.6–2.2	20.4
Short of breath doing physical activities, many times or more	0.64	0.70	2.1	1.6–2.8	22.0
Short of breath doing physical activities, a great many times or more	0.41	0.84	2.6	1.7–4.1	21.6
Cough, several times or more	0.52	0.61	1.6	0.9–2.9	15.4
Phlegm, several times or more	0.46	0.65	1.3	0.9–1.9	14.9
Chest findings
Wheezes/rhonchi	0.36	0.86	2.7	1.6–4.1	25.4
Crackles	0.09	0.90	0.9	0.3–2.5	10.8
Diminished breath sounds	0.57	0.88	4.7	3.2–6.9	38.5
Prolonged expiration	0.43	0.88	3.7	2.3–5.7	32.8
Hyperresonance to percussion	0.39	0.94	6.7	3.8–12.0	47.2
Any of the five chest signs	0.82	0.67	2.5	2.0–3.1	24.8

Note: The overall prevalence of severe COPD was 11.7%.

Abbreviations: COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; LR, likelihood ratio; CI, confidence interval (for LR); PPV, positive predictive value.