Interpretation of the "positive" methacholine challenge.
BACKGROUND
A methacholine challenge may be used in confirming the diagnosis of asthma, occupational asthma, or reactive airways dysfunction syndrome (RADS) through identification of bronchial hyperreactivity (BHR). While sensitivity of the test in diagnosing clinically significant asthma is excellent, specificity of the test is poor. Since there are many conditions which have been associated with BHR, a positive test must be interpreted cautiously.


METHODS
This paper reviews potential causes of a positive methacholine challenge other than asthma or RADS which have been reported in the medical literature.


RESULTS
Factors which may be associated with a positive methacholine test include test methodology, normal variation of BHR in the general population, and numerous medical conditions.


CONCLUSIONS
In cases of inhalation exposure evaluations, alternative explanations must be considered when determining whether a causal association exists between the exposure and a positive methacholine test result.
Hewitt
David J
DJ
Center for Toxicology and Environmental Health, LLC, North Little Rock, Arkansas. dhewitt@cteh.com
D001249:Asthma / Q000175:diagnosis*; D001327:Autoimmune Diseases / Q000175:diagnosis; D016535:Bronchial Hyperreactivity / Q000175:diagnosis*; D001985:Bronchial Provocation Tests / Q000379:methods; D016085:Bronchoconstrictor Agents; D003937:Diagnosis, Differential; D005189:False Positive Reactions; D005767:Gastrointestinal Diseases / Q000175:diagnosis; D006801:Humans; D016210:Methacholine Chloride; D009784:Occupational Diseases / Q000175:diagnosis; D012141:Respiratory Tract Infections / Q000175:diagnosis; D012680:Sensitivity and Specificity
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride