When your body senses potentially harmful unwanted substances like bacteria and viruses, your immune system works to recognise them and get rid of them.
An antigen is the name given to a marker that tells your immune system whether something is harmful or not. Antigens are found on all kinds of cells - viruses, bacteria, parasites, cancer cells and normal cells in your own body. There are molecules on the surfaces of antigens that differ from those found naturally in your body. Your immune system recognises them as foreign and makes antibodies to target and destroy them.
Another name for antibodies is immunoglobulins. Antibodies are classified into five groups. One of these is IgE – or immunoglobulin E. Unlike most of the other antibodies, IgE is normally found in very small amounts in the blood. If you have an allergic reaction, you make more IgE antibodies and there will be higher levels than normal in your blood.
Allergies occur when your immune system reacts to things that are typically harmless to most people – things like grass seeds, pollen, dust mites, mould, pets, and certain foods like nuts, eggs, and fish.
The first time you are exposed to an allergen (such a peanuts or pollen) you are unlikely to have a reaction, but you become sensitised.
The next time you are exposed to the same allergen, immune cells called B cells recognise the allergen, signal to plasma cells which produce IgE antibodies, and then this triggers a series of reactions including the release of histamine and other chemicals that cause your symptoms.
How is IgE testing used?
Typically, a skin prick test is used first. Blood tests for IgE antibodies are done if the skin prick test does not give conclusive results or if for any reason it cannot be performed. These are a type of antibodies normally found at low levels in your blood, but which increase if you have an allergic reaction.
A skin prick test is used to diagnose an allergy but sometimes the results are inconclusive, or else the test cannot be done because you have a skin condition such as dermatitis or eczema, or you are taking a medication that could interfere with the results. It may be because of the risk that you could experience a dangerous allergic reaction to skin prick testing. It is important to let your medical team know about any health conditions you have or any medication you are taking.
Types of IgE antibody tests
There are two main types of IgE antibody tests used to look for an allergy.
| Total IgE test | Your doctor may start by ordering total IgE especially if they are unsure about the cause of your symptoms. This measures the total amount of IgE antibodies in your blood. However, total IgE can be raised when you do not have an allergy. |
| Specific IgE test | This measures how much IgE your body makes in response to individual allergens. You may have a specific IgE test for a single allergen such as peanuts or for a group of allergens. Typical groups include dairy or seafood food panels or weed, grass and mould panels. Alternatively, you and your doctor may pick and choose selectively from a list of allergens suspected of causing your allergies. |
Sample
Blood.
Any preparation?
None.
Testing your blood for IgE antibodies can help in making a diagnosis although it cannot give a conclusive result by itself. Higher than normal amounts of IgE antibodies can be caused by other health conditions especially infections such as parasite infection, HIV, and Epstein–Barr virus among others. Even smoking can increase your IgE.
Sometimes, other blood tests are used that can help build more evidence. These include the full blood count and the white blood cell differential which looks for the white blood cells triggered by your immune system, specifically your eosinophils and basophils. Higher amounts of these cells may suggest an allergy.
If your total or allergen-specific IgE level is within the expected range for healthy people it indicates that you are less likely to have a true IgE related allergy to a specific allergen, but the results of the test must always be interpreted by your doctor.
High levels of IgE usually indicate an allergy, but even if you are IgE positive for a specific allergen, it does not mean you will necessarily have an allergic reaction when exposed to that substance. Also, these tests cannot tell you how severe your symptoms will be.
If your test results are negative for an IgE allergy and your symptoms persist, further investigation may be needed. You could have a hypersensitivity such as Coeliac disease (sensitivity to gluten in the diet), or an enzyme deficiency, such as lactase deficiency which causes lactose intolerance.
These are autoimmune disorders in which the immune system attacks the body's own cells such as in joints, intestines or skin. With allergies, the immune system recognises food or pollen as dangerous and reacts like it does when trying to kill a virus or bacteria.
Alternatively, you may have an allergy-like condition that is not mediated by IgE for which there are no specific laboratory tests. It is important to investigate your personal situation with your doctor’s assistance.
Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.
Some of your results are shown in your report as a comparison against a set of numbers called reference intervals or reference ranges. This is the range of test results considered ‘normal’ for the general population. If a result in your report is outside this range, it can be flagged as high (H) or low (L). This does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.
Although children do outgrow some allergies, adults usually do not. Allergies that cause the worst reactions, such as anaphylaxis when your immune system releases a flood of chemicals that cause your body to go into shock, do not usually go away. Avoidance of the allergen and advance preparation for accidental exposure in the form of medications such as antihistamines and portable adrenaline injections, is the safest course.
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:
Pathology and diagnostic imaging reports can be added to your My Health Record.
You and your healthcare provider can now access your results whenever and wherever needed. Get further trustworthy health information and advice from healthdirect.