Study objectives: The validity of peak expiratory
flow variation (PEFvar) as defined by National Heart, Lung, and
Blood Institute (NHLBI) guidelines as a diagnostic tool for suspected
asthma or its comparative value to methacholine inhalation challenge
(MIC) or postbronchodilator (BD) FEV1 responses has not
been formally assessed. We prospectively analyzed the correlation of 28
different PEFvar indexes (including 4 NHLBI-compatible indexes) with
MIC and pre-BD and post-BD FEV1 responses in suspected
asthmatic subjects with normal findings on lung examination, chest
radiography, and baseline spirometry.
Participants were asked to record peak expiratory flow four times daily
for 2 to 3 weeks, followed by an MIC. During a minimum 6-month
follow-up period, a clinical diagnosis of asthma was made or ruled out
based on testing results and response to antiasthma therapy.
Setting: Medical school-affiliated subspecialty private
practice of allergy, asthma, and immunology.
Participants: One hundred twenty-one suspected asthmatic
patients with normal findings on lung examination, chest radiography,
and baseline spirometry.
Measurements and results:
Fifty-seven subjects completed both the peak flow diary and the MIC and
were accepted for statistical analysis. There were no statistically
significant correlations between any peak expiratory flow index and
MIC. Among the three diagnostic tools evaluated, MIC had the highest
sensitivity (85.71%). All the PEFvar indexes and post-BD responses had
low sensitivity and high false-negative rates.
Conclusions: PEFvar and post-BD FEV1 responses
are poor substitutes for MIC in the assessment of patients with
suspected asthma with normal findings on lung examination, chest
radiography, and spirometry. Our findings warrant a reconsideration of
the NHLBI guidelines recommendation of the utility of PEFvar as a
diagnostic tool for asthma in clinical practice.