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[While
searching I found this article, which is quoted often on the unreliability of
CEDS. It brought back a memory of mine. When the RAST test was new, I asked the
local ear-nose-throat expert doctor about it. He said it was no good. Two years
later I got tested at his office using the RAST test.-bfg] "Electrodermal
testing measures electric impedance on an acupuncture point and is a common
form of unconventional testing for allergies. In a double blind, randomised
block design study, Lewith et al (p 131)
evaluated how it compared with conventional skin prick testing in 30 volunteers.
Half of them had reacted positively to a previous skin prick test for allergy
to cat dander or house dust mite. The results of more than 1500 separate
allergy tests showed that electrodermal testing does not correlate with
skin prick testing and so should not be used to diagnose these allergies."
[Conclusion was interesting in that the
prick skin test is not to be used for diagnosis without a detailed patient
history AND it isn't all that accurate (see below). Also, EDS is a screening device. The doctor does
the diagnosing not the device.-bfg]
http://bmj.com/cgi/content/full/322/7279/0/b
The
study assumed skin prick testing was 100% accurate. I would have believed the
study if and only if the allergies were ones that the patients verified. I searched the internet and
found these references to the skin prick test:
"But
the accuracy of the skin prick test
can range from 30 to 63 percent, Szeinbach said."
Ohio
State University Research
http://www.acs.ohio-state.edu/researchnews/archive/noallrgy.htm
"...However,
if IgE levels are low, there may not be a wheal - indicating an allergy -
even if the person tested is sensitive to these inhalants....Since over 85
percent of food allergy is non-IgE mediated, this type of testing cannot give an
accurate picture of a person's food problems. The scratch test also cannot be
used for testing chemicals, since most chemical reactions are not IgE
mediated." - page 55
Allergy
Relief & Prevention by Jacqueline Krohn, MD
"The
prick skin test is simple, rapid to perform, highly sensitive and cheap. It is
only semi- quantitative
and unless controlled carefully can yield false positive or false negative
results. It must be kept in mind that positive skin test indicates the
presence of IgE antibody but this by itself does not mean that the individual
has an allergic disease. The prick test has largely replaced the
scratch test as it is less invasive and gives fewer false positives. The
intradermal test is more sensitive but yields more false positives"
http://www.drbarryzimmerman.com/allergy/evaluation_of_allergy.htm
"Now most doctors reckon that an accurate medical
history contributes 80% of the diagnosis, and testing the other 20%; and yet
patients often think, or would like to believe, it’s the other way round:
which may be true in some branches of medicine but it is certainly not true in
allergy at the moment.
"We would certainly like an accurate test for food
allergy. The skin prick tests (SPTs) that I mentioned earlier are a very
accurate test but only unfortunately for acute types of allergy that include
foods such as nuts, eggs, and fish, for example. In practice we have found
quite a lot of patients allergic to potatoes by this method and cutting them
out has proved effective in relieving symptoms. Unfortunately though if
eczema is associated with a food it is often not an acute reaction but rather
a delayed one and delayed reactions will not give positive SPTs.
Blood tests are
no better either: the so called RAST (CAP) tests are similar and less
accurate than SPTs. IgG4 tests available only privately maybe more helpful but
give many false positive results- more trials looking into their value are
being planned.
http://www.talkeczema.com/docs/features/feature_eczema_food_allergy_tests.htm
"It
is impossible to accurately demonstrate intolerances through conventional
testing methods."
http://www.wellness.demon.co.uk/allbro~1.htm
"As
is the case with skin tests, a direct correlation cannot be assumed between
evidence of allergen-specific IgE antibody and clinical disease.
Therefore, the interpretation of these results by the physician requires
correlation with the history and physical "examination obtained by
face-to-face contact with the patient."
http://www.jcaai.org/Param/Allergy/Aller2F.HTM
from:
Annals of Allergy, Asthma, & Immunology. Volume 75 (6), December 1995.
"Prick
testing is used for diagnosis of clinically immediate (IgE-mediated)
hypersensitivity induced by a wide variety of inhalant and food allergens.
Performing and interpreting skin tests require training and practice. It is
virtually impossible to quantify the exact amount of injected material used in
prick tests. Therefore, the reliability of the test depends on the device
used, the depth and force of the puncture needle, the duration of force, the
angle of the application device, and the stability of extracts."
"Intradermal
tests are used when prick testing is not sensitive enough to detect the cause
of an allergic reaction."
"In
general, intradermal and prick tests are safe. Possible complications
include large local reactions and, rarely, immediate systemic reactions. The
latter are more common with intradermal tests because the absorption rate is
much higher than in prick tests. The rare fatalities attributed to skin
testing have all occurred after intradermal procedures; no deaths have been
reported after prick testing."
Gerald
W. Volcheck, MD
VOL
109 / NO 5 / MAY 2001 / POSTGRADUATE MEDICINE
http://www.postgradmed.com/issues/2001/05_01/volcheck.htm
"
Unfortunately, the standardized test reagents available in Europe with known
protein and antigen content are still not commercially available in the United
States. "
http://www.infectioncontroltoday.com/articles/131feat3.html
Parents
and children were told and the children recorded in their booklet which
allergens caused a reaction on their arm. In addition, they were given a note
explaining that a reaction does not necessarily mean that an allergy to
that substance was present, and that if there was no physical reaction to
exposure then no action needed to be taken.
http://www.ich.bris.ac.uk/ALSPACext/MainProtocol/Appendix8/section3.htm
Skin
tests are used to prove sensitization. A skin test is only valid when the
result is positive. Negative skin tests do not exclude allergy.
The skin tests are scanty in reliability and not useful in nonimmunological
drug reactions.
http://www.med.nagoya-u.ac.jp/Environderm/edj/vol5/5s-68.htm
Environ
Dermatol 5 : Suppl 2 : 68-73, 1998
Limitations
False-positives: nonspecific irritant reactions; dermographism interpreted
as a wheal; hemorrhage at prick site interpreted as erythema; allergen spread
from one site to another when the same needle is reused; small wheals (eg, 2
mm) interpreted as significant; impurities or contaminants in allergen
preparations; test sites improperly spaced; inappropriate allergen
concentrations
False-negatives: waning
potency of allergens; inadequate concentration of allergen; technical errors
in epidermal puncture; drugs such as HI antagonists, hydroxyzine, tricyclic
antidepressants, phenothiazines, dopamine; skin diseases such as atopic
dermatitis; possibly extremes of age
http://www.drgenie.com/Procedures/aaa/25.htm
"Skin
prick test: Most people are familiar with allergy skin prick testing (SPT). A
positive latex SPT is a sensitive indicator of an IgE sensitization. There
is as yet no FDA-approved latex extract available for skin testing in the
United States. Dr. Robert Hamilton at the Johns Hopkins University is
leading a study of a latex extract for SPT use. The clinical trials are in the
final stages, and FDA approval of an extract is expected by the end of 1998.
Pending this outcome, some physicians are making their own extracts.
Typically, they do this by cutting a latex glove into pieces and soaking them
in saline for t5 minutes, thereby producing a viable extract. A positive
reaction is considered proof of a type I latex allergy. This sort of
testing is not recommended for a person who has already experienced a severe
type I or anaphylactic reaction to latex. Appropriate emergency equipment
must be available if a latex SPT is done."
http://www.asurefit.com/chimal_skin_shield/Latex_References_AJN.htm
"Skin
tests are of lower efficacy in the assessment of the response to low molecular
weight antigens because many of these must be conjugated to other proteins,
may act as skin irritants, and thus have higher rates of false negativity and
of false positivity, if not prepared and applied by experienced
personnel.
"Given the present state of the art of immunologic testing for
occupational asthma, such testing should be reserved for investigative
purposes, principally."
http://askwaltstollmd.com/archives/mcs/41776.html
Allergy skin
tests detect only the presence of antibodies. They cannot make an
accurate determination that an allergy exists.
The least expensive allergy skin test is the skin prick or
puncture test.
http://www.ehealthmd.com/library/foodallergies/FA_how.html
Allergy
skin tests are cheap and easy to do. However, the predictive value of these
types of tests varies depending on the patient's allergy history. For example,
it is not uncommon for patients with a strong history of food allergies to
have negative skin tests or weakly positive skin tests to specific foods that
they know cause problems. [If a food has been avoided for quite some
time, the body does not react as strongly, either - bfg] In general,
up to 50 percent of sensitive allergy patients will have a false negative
reaction. Up to 15 percent of patients with low sensitivity to the allergen
will have a false negative reaction." - pg 101
The Complete Idiot's Guide to Food Allergies
by Lee H. Freude, M.D., and Jeanne Rejaunier, Penguin Group, 2003
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