View - ResearchSpace@Auckland - The University of Auckland

a 26Vo lower total serum IgE than men, which is surprising when asthma tends to be more
prevalent in women in adulthood. There was a lack of association between the prevalence of
atopy (defined as a positive response to any of the four specific allergens used in skin prick
testing in all centres) and the geometric mean of total serum IgE. It is probable that the total
and specific IgE are influenced differently and while raised IgE is associated both with atopy
and with asthma, the relationship is not clear (Burney, Malmberg et al. 1997). Furthermore,
IgE antibody production is T cell dependent, and the immune response to allergens can also
include other immunoglobulins such as immunoglobulin Ga (IgG+) and immunoglobulin A
(IgA) which may give further variations (Platts-Mills and Heyman 2006).It is true to say that
if a child is thought to have bad asthma, but is non-atopic, then the search for an alternative
diagnosis should be undertaken immediately.
Pulmonary function tests have been one of the mainstays of assessing respiratory disease in
older children and adults. A measurement in forced expiratory volume in I second (FEVI)
alone can miss small airway obstruction in patients and the forced expiratory flow rate over
25-75Vo of forced vital capacity (FEF25 -tsw) may well be a more sensitive indicator,
particularly in children and/or in mild disease; however, the measurement may be very
variable. Subjects can have a reduction in this parameter of more than two standard deviations
below predicted norms even with no clinical symptoms (Kercsmar 2006). There is a
significant overlap with measurements between healthy children and those with episodes of
wheeze (if not current), and the diagnostic value of baseline lung function tests is generally
thought to be poor (Dundas and McKenzie 2006). The guidelines suggest a test of
bronchodilator responsiveness for asthma either clinically and/or utilising improvement in
lung function (usually FEVr) by an arbitrary amount, sometimes 157o. Despite this, the SIGN
guideline states "a definitive diagnosis of asthma can be difficult to obtain in young children.
It is often not possible to measure ainvay function in order to confirm the presence of variable
airway obstruction" (SIGN 2005).
The other option for possible diagnosis and monitoring of asthma is to use peak expiratory
flow (PEF). This is defined as the largest expiratory flow achieved with a maximal forced
effort from a position of maximum inspiration sustained for longer than l0 milliseconds
(Wright and McKerrow 1959). PEF reflects a range of physiological characteristics including
lung elastic recoil, large airway calibre and lung volume (Ruffin Z0O4). The original .peak
Flow Meter' was pioneered by Martin Wright in 1959 (Wright and McKenow 1959) and is
now supplanted by newer models but these have retained the advantages of the original in
being low cost and easily portable. In the late 1970s the use of PEF recordings was first
13