Oral Challenge Tests
Oral challenge (oral provocation) tests are administered to diagnose a patient's possible allergy to a particular food or medication. During the administration of such a test, the patient ingests the possible allergen and is then observed for the development of allergic symptoms. An oral challenge test is generally employed after a more typical dietary method has failed to yield conclusive results.
The more typical food or medication allergy tests involve excluding the suspected allergen from the diet to see if the symptoms lessen or disappear, or the administration of blood or skin allergy tests. If these other tests are negative or inconclusive, and the intolerance to the particular food or medication is still suspected, the oral challenge test may be administered. Medications commonly suspected of resulting in patient intolerance are nonsteroidal anti-inflammatory drugs (NSAIDS) and certain antibiotics. Common food allergies include nuts, milk, and eggs.
Prior to the Oral Challenge Test
There are certain protocols followed in administering oral challenge tests. First of all, patients should be healthy when taking the test. If an upper respiratory or digestive problem is occurring, or if the patient is currently having an allergic response, the test is postponed. If the patient has suffered a life-threatening allergic reaction to the substance in question, the oral challenge test will probably be considered too dangerous to be administered.
Before the oral challenge test, the patient is instructed to:
- Avoid the suspected allergen for a week or two
- Stop taking antihistamines or other allergy suppressants
- Fast, so no other food ingredients alter the results
If the patient's risk level is considered high, the test is administered in a specially equipped research unit or in a hospital setting.
The Oral Challenge Test Procedure
The patient swallows a specific quantity of the test food or medication at designated intervals. During the examination, the patient is closely observed for any evidence of an allergic reaction. Potential allergic responses may include:
- Gastrointestinal distress
- Hives
- Itching
- Nasal irritation
- Wheezing
- Swelling of the eyes, lips, face or tongue
The oral challenge test is typically administered twice, once with a placebo substituted for the potential allergen. To make sure that the results are clinically objective, the person who labels the administered substances is not the doctor; the doctor, like the patient, remains unaware of whether the patient is, or is not, receiving the perceived allergen. Depending on the severity of the patient's allergic reaction, the patient will remain under observation for a shorter or longer period of time.
Risks of Oral Challenge Tests
The most serious risk of an oral challenge test is that the patient will have a life-threatening response, a condition known as anaphylactic shock. Other possible complications include:
- An acute asthmatic attack
- Hives (urticaria)
- Angioedema
Angioedema is a sudden swelling of the lips, skin, mucous membranes, or abdominal organs. Emergency medications and equipment are kept available during oral challenge tests so that any dangerous complications can be immediately addressed. It is possible that a positive allergic reaction may persist for many hours, or even for many days. Medications can usually be administered to decrease these symptoms until they abate on their own.
It is important that patients inform the doctor if any allergic symptoms arise after they leave the testing site.
Results of Oral Challenge Tests
Presumably, the results of the oral challenge test allow the doctor to evaluate the patient's allergic responses. The test is considered positive if the patient has a reaction to the suspected substance, but not to the placebo. Once the particular allergy has been definitely diagnosed, the patient is advised to avoid the food or medication in question. A negative response to an oral challenge test is considered conclusive.