PURPOSE: The standard methacholine challenge (MCT) for the evaluation of bronchial hyperresponsiveness is lengthy and tiresome. Several authors have proposed but never reported the use of an abbreviated protocol. The purpose of our study was threefold: describe the safety of our abbreviated protocol implemented April 2002, examine factors associated with positive MCT, and monitor for a delayed diagnosis of asthma in subjects with a negative MCT.
METHODS: A retrospective chart review of 500 subjects tested with an abbreviated five-breath method. Our abbreviated MCT consists of a placebo of buffered saline followed by escalating methacholine concentrations: 2.5mg/ml, 10mg/ml and 25mg/ml. A positive response is defined as a 20% decline from the baseline FEV in which case albuterol by nebulizer is given and spirometry repeated. The medical record was reviewed for any subsequent adverse effects up to 24 hours. We also evaluated each positive study for an exaggerated response (decrease in FEV1 >40%). Demographic data was gathered to identify factors associated with a positive response. Subjects with a negative study were followed until December 2009 or lost to follow up to identify a delayed diagnosis of asthma.
RESULTS: Nearly all subjects had follow up of at least one year. Of the 500 subjects tested there were no immediate adverse effects. Subjects with a greater than 40% decline of FEV1 experienced the same average return to baseline FEV1. There were no delayed adverse effects such as an emergency room visit or hospitalization. Finally, no patient at the follow-up visit after the methacholine challenge reported any complication. Factors associated with a positive study reflect those previously described in the literature. Four subjects were later given a diagnosis of asthma despite a negative study.
CONCLUSION: This abbreviated methacholine challenge offers greater convenience without a compromise of safety. Hopefully this will promote a greater utilization of this valuable diagnostic study.
CLINICAL IMPLICATIONS: This time efficient and convenient approach to the diagnosis of airway hyper responsiveness translates into greater cost-savings without any compromise to patient safety.
DISCLOSURE: Pedro Quiroga, No Financial Disclosure Information; No Product/Research Disclosure Information