Reference values for methacholine reactivity (SAPALDIA study).
BACKGROUND
The distribution of airway responsiveness in a general population of non-smokers without respiratory symptoms has not been established, limiting its use in clinical and epidemiological practice. We derived reference equations depending on individual characteristics (i.e., sex, age, baseline lung function) for relevant percentiles of the methacholine two-point dose-response slope.


METHODS
In a reference sample of 1567 adults of the SAPALDIA cross-sectional survey (1991), defined by excluding subjects with respiratory conditions, responsiveness during methacholine challenge was quantified by calculating the two-point dose-response slope (O'Connor). Weighted L1-regression was used to estimate reference equations for the 95th , 90th , 75th and 50th percentiles of the two-point slope.


RESULTS
Reference equations for the 95th , 90th , 75th and 50th percentiles of the two-point slope were estimated using a model of the form a + b* Age + c* FEV1 + d* (FEV1)2 , where FEV1 corresponds to the pre-test (or baseline) level of FEV1. For the central half of the FEV1 distribution, we used a quadratic model to describe the dependence of methacholine slope on baseline FEV1. For the first and last quartiles of FEV1, a linear relation with FEV1 was assumed (i.e., d was set to 0). Sex was not a predictor term in this model. A negative linear association with slope was found for age. We provide an Excel file allowing calculation of the percentile of methacholine slope of a subject after introducing age--pre-test FEV1--and results of methacholine challenge of the subject.


CONCLUSIONS
The present study provides equations for four relevant percentiles of methacholine two-point slope depending on age and baseline FEV1 as basic predictors in an adult reference population of non-obstructive and non-atopic persons. These equations may help clinicians and epidemiologists to better characterize individual or population airway responsiveness.
Jayet
Pierre-Yves
PY
Service of Pulmonology, University Hospital Lausanne, Switzerland. pierre-yves.jayet@chuv.hospvd.ch
Schindler
Christian
C
Künzli
Nino
N
Zellweger
Jean-Pierre
JP
Brändli
Otto
O
Perruchoud
André Paul
AP
Keller
Roland
R
Schwartz
Joel
J
Ackermann-Liebrich
Ursula
U
Leuenberger
Philippe
P
D017677:Age Distribution; D000465:Algorithms; D001985:Bronchial Provocation Tests / Q000379:methods / Q000592:standards*; D003936:Diagnosis, Computer-Assisted / Q000379:methods* / Q000592:standards*; D006801:Humans; D016210:Methacholine Chloride; D012016:Reference Values; D015203:Reproducibility of Results; D012130:Respiratory Hypersensitivity / Q000175:diagnosis* / Q000453:epidemiology*; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D013557:Switzerland / Q000453:epidemiology
D016210:Methacholine Chloride