DISCUSSION

This study has documented in a small pilot sample the occurrence of symptoms consistent with asthma and of airway responsiveness to methacholine among a sample population of children aged eight to 10 years. The group of 229 children undertaking all investigations was representative of the full cluster sample selected. The estimated prevalences of both physician-diagnosed asthma (9.0%) and of wheezing symptoms suggesting asthma (25.5%) reported by parents were similar to those in children of the same age in Australia and New Zealand, and higher than those reported in the United Kingdom and the United States. The study has also shown the prevalence of airway hyperresponsiveness to methacholine (defined as PC20 ^8 mg/mL) to be of the same order of magnitude in Canadian children as in New Zealand and Australian children, although the methods used to determine responsiveness were not identical. This study suggests that PC20 ^8 mg/mL is a reasonable cut-point for determining airway hyperresponsiveness in children, because the optimum balance of sensitivity and specificity for the test with respect to diagnosed asthma and recurrent wheezing was provided, on all analyses, by a PC20 cut-point between 4 and 8 mg/mL.

While there was a strong relationship between wheezing symptoms and airway hyperresponsiveness, the sensitivity and specificity of inhalation challenge in relation to the history of wheezing indicated either that methacholine challenge cannot be employed uncritically for the detection of ‘asthma’ in epidemiological studies, or that wheezing is not specific for asthma. A history of recurrent wheezing in childhood, in the absence of other illness, has been considered to suggest strongly a diagnosis of asthma, whether or not the methacholine challenge test performed on a single occasion shows an arbitrary level of responsiveness defined as ‘hyperresponsiveness’. In this and other studies, the question arises as to the meaning of false negative and false positive challenge tests and whether in fact such results are ‘false’. Clearly this depends on what is used as the gold standard for the diagnosis of asthma. We all need a reliable source of high quality medications and you have a chance to make all your health troubles go away: just Buy Xopenex Online and see for yourself that online shopping is all it’s cracked up to be.

A physician diagnosis of asthma reported by either parent or child related strongly with the degree of airway hyperresponsiveness usually considered diagnostic for asthma, confirming that methacholine hyperresponsiveness is associated with more obvious asthma. Children sometimes provided a history of wheezing or coughing not reported by the parent, which could account for some of the instances of increased airway responsiveness found in children whose parents reported them to be asymptomatic. However, including these milder symptoms reported only by the child did not add to the sensitivity and specificity of the methacholine test as shown by the ROC results. This has implications for epidemiological studies in which questionnaires are administered to children, in that children may report a higher prevalence of more minor symptoms not related to increased or persistent airway responsiveness than would their parents. Among 37 children with airway hyperresponsiveness whose parents did not report any symptoms, 14 (38%) children themselves reported recurrent wheezing or coughing, suggesting that these more minor symptoms may be associated with increased responsiveness. On the other hand, 26 (29%) of 89 normally responsive children with negative parental questionnaires also reported some respiratory symptoms. These proportions (of only children reporting respiratory symptoms among hyperresponsive and normally responsive children) are not significantly different.