RAST Test for Food Allergies in Cats

Feline allergies can be detected using different types of tests including blood tests, trials or intradermal testing. The RAST test is a blood test that may be used to diagnose allergies. However, this type of testing is not efficient in determining food or contact allergies.

The RAST Test

The RAST (radioallergosorbent) test is used in humans or pets to determine the presence of allergies (inhalant allergies or atopy). The test is performed on a blood sample. The blood will have to be tested for the presence of different antibodies which form if the cat is allergic to different factors such as pollen or chemicals. However, in the case of food allergies, there won't be specific antibodies in the blood, so the RAST test is not effective. The RAST test may take up to 2 weeks.

Even for the other types of allergies in cats, the RAST test may show a false positive, as it was created for humans and will therefore only show 100% accurate results in humans. Atopy or inhalant allergies may be diagnosed through intradermal skin testing (IDST), which will show more accurate results. However, even the IDST will may only be up to 80% accurate in finding allergies in felines. The ELISA test is similar to the RAST testing and may be used if the cat is suspected of having inhalant allergies.

Intradermal Testing

Intradermal testing (IDST) is performed by injecting different substances on small areas of the cat's skin. If the cat is allergic to a certain irritant, he will display a negative reaction on the skin area injected with that irritant. Cats that take antihistamines or steroids may not take the IDST, as the results may not be conclusive.

Food Allergy Testing

Food allergy testing is the only way to detect food allergies in cats.

The food allergies are the most difficult to identify, as the cat could be allergic to any of the compounds of his diet. Several weeks or months of food trials will be needed to successfully isolate the allergen.

During the first weeks, the cat will eat a diet that is composed of two types of food: one source of proteins and one source of fibers. These ingredients should be different from what the cat has had in his regular diet. If the cat displays no allergies, after three weeks a new ingredient will be introduced in the diet.

Every two weeks the cat will get a new ingredient and he will be closely monitored. If the cat starts to develop an allergic reaction, the allergen is detected and is the last ingredient introduced.

If the allergen is detected, the testing can continue, as the cat may be allergic to several other ingredients. A cat that is allergic to food will have a special diet, which will not include the allergens.

This is a long and complicated testing procedure, but it is the only way to identify food allergies. RAST tests cannot be used in detecting feline food allergies.