222 Diet Wise
Conventional Allergy Testing MethodsPrick or scratch tests and hyposensitization
The mainstay of conventional allergy test has not advanced
significantly since 1911, when the prick and scratch test method was first
developed. For this method a small drop of the substance being tested is
dropped onto the skin, which is then scratched or pricked with a needle
at that spot. The amount of flare and wheal compared to that caused by a
control (inert) solution gives an indication of how allergenic the substance is
(Noon L., Prophylactic Innoculation against Hay Fever, Lancet 1, London,
1911, p. 1572).
It is a very inaccurate method, with many false negatives, and
subjects seldom react to food at all in this way, though a demonstrable
allergy may be present on challenge testing.
An important migraine study at the Great Ormond Street Hospital
for Sick Children in 1983 showed that none of the cases would have
recovered by following an exclusion diet based on the results of the prick
testing included in the trial, though 93 per cent improved on a suitable diet,
showing that food allergy was the cause (Egger J. et al. Is Migraine Food
Allergy? Lancet, London, 15 Oct 1983, pp.865-8).
- False negatives: are disastrous because you are misled into believing
the substance is safe - False positives: are merely inconvenient, you avoid something
unnecessarily, when it is quite safe
One final failure, which is not talked about: the substance with the
largest reaction may not be the one which is causing you the most trouble,
as I have found out many times with the help of Miller’s Method (see later
in this chapter, page 225).
The hyposensitization method aims to find out which substances
the patient is allergic to, by giving a whole batch of prick testing, and then to
administer injections of a mixture of these, increasing gradually in strength,
until quite large amounts are being tolerated. The body is often then found
to be able to cope with normal ambient concentrations.
There are two major drawbacks to this hypo-sensitization treatment:
- it rarely works and
- it can be extremely dangerous. Patients sometimes
react severely and deaths due to anaphylaxis occurred regularly
until by common consent its use was abandoned in 1986, except in
special circumstances and where full cardio-pulmonary resuscitation
equipment is at hand.