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Airway Hyperresponsiveness to Methacholine at Age 6 to 8 Years in Nonasthmatic Patients Is Not Related to Increased Health-Care Utilization for Asthma in the Ensuing 5 Years^*

A Longitudinal Study of a Birth Cohort

^* From the Henry Ford Health System (Drs. Siwik, Johnson, Peterson, and Zoratti, and Ms. Havstad), Detroit, MI; and the Medical College of Georgia (Dr. Ownby), Augusta, GA.

Correspondence to: Jaroslaw P. Siwik, MD, Bronson Internal Medicine Associates, 2600 West Centre St, Portage, MI 49024; e-mail: siwikj{at}bronsonhg.org

Background: Children with heightened airway responsiveness have a greater tendency to develop asthma symptoms. Many existing studies describing this relationship have relied on self-reported symptoms that may be prone to recall bias. In addition, few studies have examined the relationship of airway hyperresponsiveness (AHR) to indicators of asthma severity such as health-care utilization.

Objective: To determine whether a positive response to methacholine challenge in children without current or physician-diagnosed asthma at age 6 to 8 years is predictive of the subsequent onset of asthma requiring medical evaluation or treatment in the ensuing 5 years.

Methods: Data were obtained from subjects in a population-based birth cohort (n = 835) enrolled from 1987 to 1989, who were members of a large medical group practice component of a health maintenance organization (HMO). We analyzed a subset of subjects (n = 245) who had completed a methacholine challenge at age 6 to 8 years, had no current or physician-diagnosed asthma, and were still served by the same medical group. These children were followed up from the time of methacholine challenge until HMO disenrollment or through June 2001 (ages 11 to 13 years), whichever came first. Pharmacy claims data and diagnostic codes from physician-patient encounters were evaluated for incident asthma. Incident cases of clinical asthma were defined as any child with two outpatient visits or one hospitalization, one emergency department encounter associated with an asthma diagnostic code (ie, 493.XX), or any child filling prescriptions for two bronchodilators or one antiinflammatory asthma medicine. Methacholine responsiveness was interpreted using American Thoracic Society criteria.

Results: Asthma incidence did not differ based on methacholine challenge results for children with normal, borderline, and mild AHR. No child in the study demonstrated moderate-to-severe AHR.

Conclusion: Our data suggest that AHR with a borderline or weakly positive result in a methacholine challenge in children 6 to 8 years old without current or physician-diagnosed asthma is not related to increased health-care utilization for asthma in the ensuing 5 years.

Key Words: airway hyperresponsiveness • asthma • bronchial reactivity • cohort • methacholine