Methacholine Challenge Test is designed to see if the patient’s bronchial tubes are unusually sensitive to a drug called methacholine.
Methacholine Challenge Test is considered positive if lung capacity (FEV1) drops by 20% or more with the medicine at a dose of 16mg or less. Negative test rules out asthma in most patients. Positive test suggests the patient may have asthma, but may be positive in patients with allergic rhinistis, GERD, COPD or following viral infections up to six weeks. Many family members of asthmatics may have positive methacholine challenge test without asthma.