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Asthma

Cough variant asthma

07/06/2009

Question:

My PCP thinks that I have cough variant asthma, but a pulmonolgist does not think it is asthma. I have had a methacholine test done that showed it was asthma. Could there be a reason that I would have a positive methacholine test, but a pulmonologist think it wasn`t asthma?

Answer:

The Methacholine challenge test is most helpful as a diagnostic test when it is negative because a negative test virtually eliminates the possibility of asthma (assuming it was performed properly and medications were withheld as instructed).  However, a positive response does not confirm asthma because several conditions can cause a positive test.  People with allergies (like hayfever), recent viral infection, COPD, recent chemical irritant exposure and others can be associated with a positive test.  Additionally, the test is sometimes confusing to interpret because most people will react to high doses of Methacholine but asthmatics will have a decline in airflow (FEV1) at low to moderate doses.  The amount of airflow decline and the amount of methacholine needed to cause that decline must be considered when interpreting the test. 

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Response by:

Cathy   Benninger, RN, MS, APRN, C-AE Cathy Benninger, RN, MS, APRN, C-AE
Clinical Assistant Professor
Director, OSU Asthma Center Educational Program
College of Medicine
The Ohio State University