Classes of Asthma Severity

 

Classification:

(1) intermittent vs persistent

(2) if persistent: mild, moderate or severe

 

 

Severity Class	Symptoms	Exacerbations	Nighttime Asthma Symptoms	PEF or FEV1
intermittent	< 1 time per week	brief (from a few hours to a few days); asymptomatic between exacerbations	< 2 times per month	>= 80% of predicted; variability < 20%
mild persistent	>= 1 time per week but < 1 time per day	may affect activity and sleep	> 2 times per month	>= 80% of predicted; variability 20-30%
moderate persistent	daily; daily use of inhaled short-acting beta-2 agonist	affect activity and sleep	> 1 time per week	> 60% to < 80% of predicted; variability > 30%
severe persistent	continuous; physical activities limited	frequent	frequent	<= 60% of predicted; variability > 30%

 

where:

• PEF = peak expiratory flow

 

Limitations:

• No single test or measurement can accurately classify the level of asthma severity.

• Criteria for defining disease severity are based on symptoms and changes in pulmonary function before initiation of any therapy.

• With exacerbations the severity of disease can change abruptly and dramatically.

 

Equations for Predicting PEF from Nunn (1989)

 

Peak expiratory flow for men:

 

LN(PEF in L/min) =

= (0.544 * LN(age in years)) - (0.0151 * (age in years)) - (74.7 / (height in cm)) + 5.48

 

Peak expiratory flow for women:

 

LN(PEF in L/min) =

= (0.376 * LN(age in years)) - (0.0120 * (age in years)) - (58.8 / (height in cm)) + 5.63

 

Equations for FEV(1) from Crapo (1981)

 

predicted FEV(1) in liters for males =

= ((0.0414 * (height in cm)) + ((-0.0244) * (age in years)) - 2.190

 

predicted FEV(1) in liters females =

= ((0.0342 * (height in cm)) + ((-0.0255) * (age in years)) - 1.578