Diagnosis of Food Allergy

Food allergy are typically diagnosed with one or a combination of the following methods:

When diagnosing which food could be giving you an allergic reaction, the doctor will asked you for a detailed history of what food you have taken when you have attack. Things like the how soon after you have eaten a certain food did you get the attack, is it within minutes or an hour after. Do you always get the same reaction after eating certain foods? Did anyone else feel ill after eating the same food as you? How much food did you eat and do you know how and where the food is prepared?  Knowing all these facts can help the doctor decide if you need further diagnosis and the possible course of treatment. 

Food Elimination Diet 

Sometimes, it is difficult to pinpoint which is food or foods are making your body react. A popular method of diagnosis food allergies is an elimination diet. By removing certain foods from your diet, there is a chance of finding the offending food. For example, if you suspect that egg is the allergen, remove eggs from your diet, observed if the symptoms have disappeared. Eat the food (egg) again and if the symptoms come back, you can confirm that it was eggs that you are allergic to. The process of food elimination to determine your food allergies can be tedious and time consuming. You need lots of patience and determination as it is possible to have an allergic reaction to more than one type of food. Elimination diet is usually carried out if the allergic reaction is not severe and it should be conducted under the guidance of a medical professional.  

Skin Prick Testing. 

In Skin Prick Testing, the skin is subjected to suspected allergen in an attempt to provoke a small and controlled allergic response. This method involves pricking the surface of the skin and placing a drop of solution (a mixture of liquid and the suspected allergen) into the skin. Skin Prick Test is usually done on the inner forearm and more than 3 allergens may be placed on the skin in a test session.

The test measures the specific IgE antibodies in the skin when it’s subjected to the suspected allergens. A positive reaction would mean that the skin in the area will itch and becomes red and swollen with a weal in the centre within a few minutes. The weal which will expand to a maximum size in about 15 minutes should clear within an hour for most people.

Skin Prick testing is usually recommended when an allergy is suspected. It is not recommended for people with a history of severe allergy reaction. Patients are also advised not to take antihistamines for several days before the test as it may not give an accurate result. Skin Prick Tests should be carried out by medical professionals like doctors and nurses. This is to ensure that the patient gets immediate treatment in the event of any side effects that may arise.

Blood Tests 

Blood test is another popular method used in allergy testing. It is often recommended when skin prick testing is unsuitable or when the patient is taking medications such as antihistamines. Unlike Skin Prick Test, blood test does not trigger an allergic reaction, what it does is measuring the IgE antibodies that are circulating in the blood, to identify the allergens. This is especially useful for patient with skin condition such as eczema or patient with severe allergic reaction. 

There are two types of blood test- the Radioallergosorbebt test (RAST) and the enzyme linked immunisorbent assay test (ELISA). Both involved a simple procedure of taking a small amount of blood from the allergy sufferer and it will be analysed in a laboratory for any raised level of IgE antibodies. If high levels of IgE antibodies are found in the blood, it indicates that there is an allergic reaction. 

Nowadays it is possible to buy home IgE test kit for self testing. However, the result of such home test may not give an accurate reading and unlike food intolerance test kit, the blood sample are not sent to a laboratory for analysis. To get the best result from IgE blood test, it should be carried out by medical professionals.