Al­ler­gy test­ing mea­sures how a per­son re­acts to spe­cif­ic al­ler­gens, such as tree pollen, pet dan­der, foods, med­ica­tions or mould. A "pos­i­tive" al­ler­gy test means that a per­son has a spe­cif­ic al­ler­gic an­ti­body to the sub­stance test­ed. This of­ten means that the per­son is al­ler­gic to the sub­stance, mean­ing that the per­son will ex­pe­ri­ence symp­toms when ex­posed to the al­ler­gen. How­ev­er, a pos­i­tive al­ler­gy test does not nec­es­sar­i­ly mean that the per­son is in­deed al­ler­gic to the sub­stance. A per­son may have a pos­i­tive al­ler­gy test to dog dan­der, for ex­am­ple, but ex­pe­ri­ence no symp­toms with ex­po­sure to dogs. In ad­di­tion, a per­son may have mul­ti­ple pos­i­tive food al­ler­gy tests, but be able to eat these foods with­out any bad re­ac­tions.

There­fore, an al­ler­gist is need­ed to per­form and in­ter­pret al­ler­gy tests based on the per­son's symp­toms.

There are on­ly two types of al­ler­gy test­ing con­sid­ered to be valid, skin test­ing (prick/punc­ture and in­tra­der­mal) and RAST (ra­dioal­ler­gosor­bent test). Oth­er tests for al­ler­gies may be per­formed in re­search set­tings (such as plac­ing small amounts of al­ler­gen in the eye, nose or lungs to mea­sure an al­ler­gic re­sponse), but are not help­ful for every­day use. Patch test­ing is not used to test for al­ler­gy, but for con­tact der­mati­tis to var­i­ous chem­i­cals, which is due to an­oth­er part of the im­mune sys­tem.

Nu­mer­ous oth­er tests are per­formed by non-al­ler­gy prac­ti­tion­ers, or peo­ple who call them­selves "al­ler­gists" but lack for­mal train­ing and na­tion­al board-cer­ti­fi­ca­tion in the field of al­ler­gy and im­munol­o­gy. Al­ways see a for­mal­ly-trained, board-cer­ti­fied or board-el­i­gi­ble al­ler­gist when hav­ing al­ler­gy treat­ments.

What is skin test­ing?

Skin test­ing is the old­est and most re­li­able form of al­ler­gy test­ing. This form of test­ing has been per­formed for 100 years and con­tin­ues to be the test­ing of choice for the di­ag­no­sis of al­ler­gic dis­ease.

Test­ing be­gins with a prick, punc­ture or scratch method, which in­volves the plac­ing a drop of the al­ler­gen in ques­tion (usu­al­ly a com­mer­cial­ly avail­able ex­tract of pol­lens, molds, foods, pet dan­der, etc) on the skin and abrad­ing the skin with a nee­dle. This test­ing is not painful, and gen­er­al­ly there is no bleed­ing in­volved since the nee­dle on­ly scratch­es the sur­face of the skin.

Af­ter the skin is scratched, the tests takes about 15 min­utes to de­vel­op. There may be many skin tests per­formed, de­pend­ing on the per­son's age, symp­toms and oth­er fac­tors. A pos­i­tive skin test ap­pears as a raised, red itchy bump, sim­i­lar to a mos­qui­to bite. The test is com­pared to the pos­i­tive and neg­a­tive con­trols, which are two oth­er skin tests placed along with the al­ler­gens to be test­ed. The pos­i­tive con­trol is usu­al­ly his­t­a­mine, which will cause a raised, itchy bump in any­one who is not tak­ing an an­ti­his­t­a­mine med­ica­tion. It is not pos­si­ble to be al­ler­gic to his­t­a­mine, as this chem­i­cal is present in the body. A pos­i­tive his­t­a­mine skin test means that any skin tests per­formed at that same time with a neg­a­tive re­sult are in fact, tru­ly neg­a­tive (and that the neg­a­tive re­sult was not just due to the per­son tak­ing an an­ti­his­t­a­mine, for ex­am­ple).

The neg­a­tive con­trol is usu­al­ly a salt wa­ter, or saline, sub­stance. The pur­pose of this test is to en­sure that a per­son does not have an ir­ri­tant ef­fect from the prick­ing of the nee­dle. A neg­a­tive skin test re­sult to the neg­a­tive con­trol en­sures that the pos­i­tive skin test re­sults are not due to an ir­ri­tant ef­fect from a per­son with very sen­si­tive skin. If the prick skin test re­sults are neg­a­tive to var­i­ous al­ler­gens, but a per­son's his­to­ry of al­ler­gies sug­gest that these re­sults should be pos­i­tive, then an­oth­er test, called an in­tra­der­mal skin test, can be per­formed.

In­tra­der­mal skin test­ing, which in­volves the in­jec­tion of a di­lut­ed al­ler­gen ex­tract un­der the top lay­er of the skin with a nee­dle, may be able to di­ag­nose more peo­ple with al­ler­gic dis­ease than with the prick test alone. Un­for­tu­nate­ly, in­tra­der­mal skin tests may cause more false pos­i­tive re­sults, and these tests can­not be used in test­ing for food al­ler­gies. A skin test rep­re­sents al­ler­gic dis­ease in minia­ture. It is a use­ful tool for peo­ple to see (and feel) their pos­i­tive skin test to cat dan­der, for ex­am­ple, to tru­ly un­der­stand that they are al­ler­gic to cats. This ed­u­ca­tion­al ex­pe­ri­ence is much more dra­mat­ic than hand­ing a per­son a re­port of a pos­i­tive cat al­ler­gy test per­formed us­ing a blood test.

A skin test rep­re­sents al­ler­gic dis­ease in minia­ture. It is a use­ful tool for peo­ple to see (and feel) their pos­i­tive skin test to cat dan­der, for ex­am­ple, to tru­ly un­der­stand that they are al­ler­gic to cats.