INTRODUCTION
As many as 70-80% of children with asthma develop their first symptoms
before the age of 51. An early diagnosis of asthma is
crucial for several reasons: the increase in
asthma incidence in recent decades
has been principally explained by rising asthma rates in children
<3 years old2; significant declines in lung
function in may occur during the preschool years; and overall asthma
morbidity (activity limitation, sleep disturbance, urgent care and
emergency department [ED] visits, and hospitalizations) is higher in
young children than in older children and
adolescents3.
Several wheezing phenotypes coexist at the preschool age. Therefore,
despite the importance of an early diagnosis, identifying which
preschoolers with recurrent wheeze have asthma –as opposed to other,
transient causes of wheezing– remains a significant challenge. Several
factors make the diagnosis of asthma difficult in this age group,
including the fact that parents frequently report wheezing as a
catch-all term for respiratory sounds or noisy breathing. Direct
observation by a physician and assessment of bronchodilator response is
very useful, but objective measures of lung function and reversible
obstruction are difficult in young children.
There are several models in preschoolers that attempt to predict an
asthma at school and adolescent ages4. Among these,
the asthma predictive index (API)5 is widely utilized
because it is simple, inexpensive, minimally invasive, and it has been
validated in several independent populations4. The API
has a compelling positive
likelihood ratio (LR
~7.4 when applied by 3 years of age, for predicting a
diagnosis of asthma by age 6), making it helpful in the identification
of children at high risk for asthma; but its negative LR
(~0.75) is less helpful in ruling out the risk of
incident asthma4. A recent cross-sectional study in
preschoolers reported that the questionnaire-based diagnosis of asthma
is associated with a positive API6. Our hypothesis is
that the API could be used as a surrogate for asthma diagnosis in
preschoolers from a longitudinal birth cohort.