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ALLERGY TESTS: CONTROVERSIAL TESTS

 

Within the field of clinical ecology, doctors have developed four more allergies testing techniques - all highly controversial, but showing some promise nonetheless.

Intradermal skin titration is much like traditional skin testing, but with a slight twist. Instead of using a standardized test dose, testing begins with a weak dose and measures the weal prod­uced by each subsequent dose, until reactions reach a plateau and weals no longer grow progressively larger. Doctors who use this technique say that it not only determines the degree of sensitivity to the substance but also indicates how strong the treatment dose should be. (To eliminate the power of sugges­tion, patients aren't always told what they're being tested for.)

Intradermal provocation is a variation of intradermal titration. The idea is to produce not only a weal-and-flare but symptoms - which are then immediately neutralized with subsequent injections of the diluted solution. Patients may also be sent home with pre-measured doses of the allergen - either to neutralize unpleasant reactions or to prevent them.
Mainstream allergy doctors who've tried these alternative methods of skin testing claim they do not give consistent, accurate information - contrary to what the tests' advocates claim. Doctors familiar with those same tests, however, say that other doctors get poor results because they don't follow the procedures correctly.

Sublingual (under-the-tongue) provocation is used primarily to identify allergy to foods and sometimes allergy to inhalants. Extracts are mixed half-and-half with glycerin and squirted under the tongue. If nothing happens within ten minutes, the next food is tested. If symptoms develop, neutraliz­ation is attempted with dilutions of the same food extract.
Over a series of several visits, dozens of foods can thus be tested - up to thirty or forty is usually adequate. You might say that sublingual provocation is comparable with a deliberate challenge with the food itself. And it's very controversial: the few doctors who use the sublingual method swear by it, saying it works very well and is just the ticket for fidgety children or people who hate needles. Traditional doctors who've tried sublingual testing say they can't get accurate results.

The cytotoxic test (or leukocytotoxic test) is also used to detect food allergy. A sample of blood is drawn and cells are added to a mixture of sterile water, and then applied to microscopic slides smeared with food extracts in a base of petroleum jelly. The slides are examined several times - within ten minutes, after thirty or forty minutes, after one hour, after one and a half hours and after two hours. Certain changes in blood cells are interpreted as a sure sign of allergy to the food smeared on the slide.
The big plus of cytotoxic testing is that doctors claim they can diagnose allergy to many, many foods from one sample of blood. The problem, though, is that cytotoxic testing may not be as reliable or valid as its proponents crack it up to be.
'It may be reliable in the sense that two different lab tech­nicians doing the same test on the same individual may get roughly the same result,' says Iris Bell, at San Francisco Veterans Hospital and the University of California at San Francisco. 'But there's not a lot of good evidence that it's valid - that a positive test really means you can't eat the food.'
'In other words,' continued Dr Bell, 'if the cytotoxic test shows you are sensitive to fifty items - and some show that - the question is, Can you really not eat all those foods without getting symptoms?' Conversely, the test may show no reaction to a food to which you are blatantly allergic. In other words, the cytotoxic test has the same potential (or possibly more) for false positive results as does the traditional skin test.
An additional drawback of the cytotoxic test is that it gives no indication of type of sensitivity, even when the test is accurate. 'There's no way to tell from looking at a slide if you're going to get a life-threatening asthma attack or break out in one hive,' says Dr Bell.
At present, the cytotoxic test is no better than skin tests in diagnosing allergy. In fact, in some ways cytotoxic tests are less, accurate than skin tests.
'I see the cytotoxic test at the level it's been developed right now as being able to offer a hint that something may be going on,' Dr Bell says. 'But I don't think it can be used to tell you what you absolutely can and cannot eat.'
As this brief review clearly shows, allergy testing is not an exact science. Try as they might, doctors cannot always tell exactly what's going on in an allergic body. One thing that all these tests have in common is that they must be correlated with a complete and thorough medical history if they are to be interpreted correctly. No matter how sophisticated the tests become, there's no substitute for a doctor asking you for details about your diet and the environment in your home, school or workplace.
'My advice to young doctors is to listen to what the patient says,' offered Dr Constantine J. Falliers, an allergist and asthma specialist in Denver, Colorado. 'You can learn more from that than from doing the most expensive, fancy tests.'

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ALLERGIES


 

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