We are happy to provide links to the following guidelines that address the use of methacholine challenge testing:

American Thoracic SocietyGuidelines for Methacholine and Exercise Challenge Testing – 1999
(Published in American Journal of Respiratory & Critical Care Medicine, Vol. 161:1, January 2000 pp. 309-329)
The National Heart, Lung, and Blood Institute (NHLBI)
AARC Clinical Practice Guidelines
Methacholine Challenge Testing
2001 Revision & Update
The ACCP Clinical Practice Guidelines
Diagnosis and Management of Cough
(Published in CHEST Journal 129.1, January 2006 Supplement (pp. 222 – 231).

“In patients whose chronic cough persists after treatment for UACS, the possibility that asthma is the cause of cough should be worked up next. The medical history is sometimes suggestive, but is not reliable in either ruling in or ruling out asthma. Therefore, ideally, BPC, if spirometry does not indicate reversible airflow obstruction, should be performed in the evaluation for asthma as a cause of cough.”

Chronic Cough Due to Asthma ACCP
Evidence-Based Clinical Practice Guidelines
Peter V. Dicpinigaitis, MD, FCCP, 10.1378/chest.129.1_suppl.75S CHEST January 2006 vol. 129 no.1 suppl 75S-79S