re: metacholine challenge

[tasci]

Hi Dr., in response to your earlier question: This is the results of the provocholine(r) challenge test. we started at 0.025 and went up to 25.00, FVC was 101% premeasurement, and only changed 1%. FEV1 108% premeasurement and only changed 1%. FEF25-75% 123% premeasurement, changed 9% to 111%. PEF was 137% changed 3%. They are saying it is conclusive enough for not having asthma, I stopped the flovent about a week before the test. I hadn't taken any bronchodilators for about 1 month before the test. could you please give me any input if I need to retake the test a month or two later from now.

thank you

[David Tinkelman, M.D.]

The results you list, with a negative airway response to a methacholine dose of 25.0 is clearly a negative test by accepted criteria.  It is known that the full beneficial effect of Fluticasone may not be evident for 3 weeks or more after initiation of therapy.  Studies suggest that the asthmatic airway response to methacholine may be blunted by an inhaled steroid but I could not find evidence for how long.  I would be surprised if it were the case one week after discontinuation of the drug.

The following is taken directly from the Textbook,  Adkinson’s:  Middleton’s Principles of Allergy:  Principles and Practice.

“Non-selective challenges, both direct and indirect, are most widely recommended as diagnostic tests for asthma, primarily in subjects with symptoms and normal resting expiratory flow rates. Unfortunately, this statement is rather oversimplified and may be subject to misinterpretation. The direct challenges, primarily methacholine, are the most widely used. Direct challenges are highly sensitive provided symptoms are clinically current.[10,34] The high sensitivity correlates with a very high negative predictive value, indicating that a negative methacholine challenge should rule out clinically current asthma with reasonably certainty. There are a number of potential explanations for a false-negative methacholine challenge with regard to a diagnosis of asthma, as outlined in Table 73.3. These include elite or high-intensity athletes who may have EIB with a negative methacholine challenge (which is otherwise a relatively uncommon combination in the average clinical asthmatic); unrecognized or unreported use of inhibiting bronchodilator medications, including non-respiratory medications with anticholinergic effects (antidepressants, antipsychotics, etc.); lack of current exposures or symptoms; and inhalation of methacholine by a TLC breathhold method.”

[ill13632]

I have asthma that doesn't respond to symbicort- does this test tell you if you have asthma?
my FEV1 is stuck at 73% for over a year now