Bronchial hyperresponsiveness in childhood: A narrative review

Table 1 Cut-off points used to define bronchial hyperresponsiveness in children

Stimulus	Definition	Cut-off point	Ref.
Methacholine PD20	Severe BHR	PD20: ≤ 1 μmol	[19,31]
	Mild to severe BHR	PD20: ≤ 8 μmol	[19,31]
	Any BHR	PD20: ≤ 16 μmol	[19]
	BHR	PD20: < 3.91 μmol	[20]
Methacholine PC20	BHR	PC20: ≤ 8 mg/mL	[18]
	BHR	PC20: < 2 mg/mL for children between 6 to 9 yr	[22]
	BHR	PC20: < 4 mg/mL for children between 10 to 14 yr	[22]
Exercise	BHR	> 15% fall in FEV1 after exercise	[21] [30]
	EIB	> 10% fall in FEV1 after running	[25]
	AHR	A fall in FEV1 of 1.96 standard deviations more than in healthy children	[26]
	BHR	≥ 8.6% fall in FEV1 after exercise	[32]

AHR: Airway hyperresponsiveness; BHR: Bronchial hyperresponsiveness; EIB: Exercise-induced bronchial constriction; FEV₁: Forced expiratory volume in one second; PC₂₀: Concentration causing a 20% reduction in FEV₁; PD20: Dose causing a 20% reduction in FEV₁.