TABLE 4.

Association between symptoms for which subjects were referred and the result of methacholine testing

Symptom	Predictive value, %		P
	Positive	Negative
Dyspnea (n=267)
PC20<2 mg/mL	14.6	94.0	0.01
PC20<8 mg/mL	33.0	82.7	0.001
PC20≤16 mg/mL	49.4	67.7	0.001
Cough (n=307)
PC20<2 mg/mL	12.4	90.3	0.48
PC20<8 mg/mL	28.3	74.2	0.63
PC20≤16 mg/mL	43.3	54.8	0.75
Wheezing (n=199)
PC20<2 mg/mL	18.1	94.5	<0.001
PC20<8 mg/mL	35.7	80.1	<0.001
PC20≤16 mg/mL	52.3	64.7	0.001
Chest tightness (n=185)
PC20<2 mg/mL	15.7	91.6	0.02
PC20<8 mg/mL	34.6	78.1	0.005
PC20≤16 mg/mL	50.3	61.9	0.02

PC₂₀ Provocative concentration of methacholine causing a 20% fall in forced expiratory volume in 1 s