Kathy Crankshaw asked:

>I'd like information on different allergy tests
>(RAST, Allerscan etc) and how reliable the tests are.

A good overview of this:

Newsgroup: alt.support.food-allergies
Subject: Re: BEST FOOD ALLERGY TEST????????????????
From: [log in to unmask] (Jack Campin)
Date: 12 Mar 1997 01:37:04 GMT

[log in to unmask] (TICKYUL) writes:
> I am going to get tested for food allergies and would like to know of
> the best food allergy test available.  If you can shed some light on the
> subject I would be grateful.

I don't think there is a "best" test.  What there is:

- skin scratch/patch tests.  They only identify IgE-mediated allergies,
  and don't do a very good job of classifying their severity, and often
  give results misleading in both directions (reporting allergies that
  don't exist and failing to find those that do) but they're quick, cheap
  and cover a lot of things at once.

- cytotoxic blood tests.  Pretty crude and inaccurate, and vary all over the
  place if you repeat them, but cover a wide range of types of reaction -
  primarily IgG (immune responses) but maybe some funny stuff we don't
  understand yet and which more precise tests miss.

- ELISA tests.  Very selective, work for IgE, IgG, and Candida-specific IgA,
  expensive, measure severity of reactions, but quite new and so there isn't
  a lot of clinical experience in interpreting the results.  Maybe the wave
  of the future.  Also work for detecting Helicobacter pylori, the bacterium
  responsible for stomach ulcers.

- radioallergosorbent tests (RAST).  Detects IgE and related allergies.
  See Brostoff and Gamlin's _The Complete Guide to Food Allergy and
  Intolerance_ for more information about these.  I don't think they're
  widely used at present; since they involve the lab in handling mildly
  radioactive materials they must be a pain in the bum from a regulatory
  standpoint.

- hair testing.  Worthless crank mumbo-jumbo.  (But hair analysis *can*
  give useful information about nutrient deficiencies and some kinds of
  chronic poisoning, if it's done right).

If you have a serious problem with multiple foods (as most people with IgG-
related intolerances will) you can expect the severity of your reactions
to vary with time, depending on how much of the offending foods you eat.  A
bad test result doesn't always mean a total lifetime restriction.  A series
of tests taken over months or years as your diet changes will give you a
better idea of what matters and what doesn't.