Body mass index-percentile and diagnostic accuracy of childhood asthma

To determine whether high BMI-percentile is associated with misdiagnosis of asthma among children referred to an asthma specialist.

We queried the electronic records of children 8 to 18 years of age seen by a Nemours pediatric pulmonologist. All visits during a 6-year period with the chief complaint of asthma, or an asthma-like symptom such as wheeze, cough, or dyspnea, were included. We collected spirometry, blood counts, and immunoglobulin E (IgE) if available. We determined whether the child had referring physician-diagnosed asthma, specialist-diagnosed asthma, or both. Specialist-diagnosed asthmatics who met additional objective "gold-standard" criterion were labeled strict-criterion asthma.

Prevalence of high BMI-percentile was extremely common in all defined asthma groups, even those meeting strict criteria for diagnosis. Referring physician-diagnosed asthmatics did not have higher rates of obesity, and referring physician-diagnosed asthmatics had objective indicators of asthma that were the same as asthmatics diagnosed by a specialist. There was good diagnostic correlation between referring physicians and asthma specialists that was not affected by BMI. Among specialist-diagnosed asthmatics, increased BMI-percentile associated with significantly reduced forced expiratory volume in 1 second (FEV(1)), forced expiratory flow during the middle half of the forced vital capacity (FEF(25 - 75)), and FEV(1)/forced vital capacity (FVC); and significantly increased total blood leukocytes, neutrophils, and platelets compared to leans. For all 2,258 referrals, the estimated odds ratio of receiving a specialist-diagnosis of asthma increased by 0.4% with each increasing BMI percentile.

Referring physicians do not appear to erroneously diagnose children with asthma due to overweight status. Our data confirm that overweight status is extremely high in children with true asthma and likely increases the risk for true asthma. Although these data cannot discern causality, high BMI-percentile is associated with greater airflow obstruction and elevated markers of systemic inflammation that could contribute to underlying mechanisms of asthma.