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Why am I having this test?

Allergy blood testing is used to help diagnose specific allergies. An allergy occurs when your body's defence system (immune system) is more sensitive to certain substances. The immune system overreacts to the substance, causing allergy symptoms. You may have this test to help find out what is causing symptoms such as:

• Rashes
• Runny nose.
• Sneezing
• Asthma flare-ups.

Blood testing is often used when skin testing for allergies is not an option.

What is being tested?

This test measures the level of immunoglobulin E (IgE) in your blood. IgE is a type of protein (antibody) that the body produces in response to an allergen. An allergen is a substance that you are allergic to. Testing can determine exactly what allergen affects you. A common method used to measure IgE is the radioallergosorbent test (RAST) in which specific allergens are tested. You can be tested for various allergens, including:

• Animal dander.
• Food
• Pollens, dusts, and moulds.
• Latex
• Insect venoms.
• Medicines

What kind of sample is taken?

A blood sample is required for this test. It is usually collected by inserting a needle into a blood vessel.

How do I prepare for this test?

Some medicines can affect test results. Your healthcare provider will let you know when to stop taking those medicines and when you can begin taking them again.

Tell a healthcare provider about:

• Any allergies you have, especially if you have ever had a severe allergic reaction.
• All medicines you are taking, including vitamins, herbal medicines, eye drops, creams and over-the-counter medicines.
• Any medical conditions you have.

How are the results reported?

Your test results will be reported as values or RAST ratings. Your healthcare provider will compare your results to normal ranges that were established after testing a large group of people (reference ranges). Reference ranges may vary among labs and hospitals. For this test, common reference ranges are:

Reference ranges for IgE:

• Adult: 0–100 IU/mL.
• Child 0–23 months: 0–13 IU/mL.
• Child 2–5 years: 0–56 IU/mL.
• Child 6–10 years: 0–85 IU/mL.

Reference ranges for RAST:

• RAST rating 0: IgE level less than 0.35 kU/L.
• RAST rating 1: IgE level 0.35–0.69 kU/L.
• RAST rating 2: IgE level 0.70–3.49 kU/L.
• RAST rating 3: IgE level 3.50–17.49 kU/L.
• RAST rating 4: IgE level 17.50–49.99 kU/L.
• RAST rating 5: IgE level 50–100 kU/L.
• RAST rating 6: IgE level greater than 100 kU/L.

What do the results mean?

IgE levels increase when a person with an allergy is exposed to the allergen. The higher the IgE level in a RAST test, the higher the likelihood of an allergy to that allergen. A RAST rating of:

• 0 means that you have an absent or undetectable allergen-specific IgE.
• 1 means that you have a low level of allergen-specific IgE.
• 2 means that you have a moderate level of allergen-specific IgE.
• 3 means that you have a high level of allergen-specific IgE.
• 4 means that you have a very high level of allergen-specific IgE.
• 5 means that you have a very high level of allergen-specific IgE.
• 6 means that you have an extremely high level of allergen-specific IgE.

Talk with your healthcare provider about what your results mean.

Questions to ask your healthcare provider

Ask your health care provider, or the department that is doing the test:

• When will my results be ready?
• How will I get my results?
• What are my treatment options?
• What other tests do I need?
• What are my next steps?

Summary

• Allergy blood testing is used to help diagnose specific allergies.
• This test measures the level of IgE in your blood. IgE is an antibody that the body produces in response to an allergen.
• A common method used to measure IgE is the radioallergosorbent test (RAST), in which specific allergens are tested.
• Allergens that may be tested include animal dander, foods, pollens and latex.

This information is not intended to replace advice given to you by your healthcare provider. Make sure you discuss any questions you have with your healthcare provider.

References:

Gomes-Belo, J., Hannachi, F., Swan, K. and Santos, A.F., 2018. Advances in food allergy diagnosis. Current pediatric reviews, 14(3), pp.139-149.

 Lavine, E., 2012. Blood testing for sensitivity, allergy or intolerance to food. Cmaj, 184(6), pp.666-668.

Muthupalaniappen, L. and Jamil, A., 2021. Prick, patch or blood test? A simple guide to allergy testing. Malaysian family physician: the official journal of the Academy of Family Physicians of Malaysia, 16(2), p.19.

 Siles, R.I. and Hsieh, F.H., 2011. Allergy blood testing: a practical guide for clinicians. Cleve Clin J Med, 78(9), pp.585-592.

For allergy blood test services, contact:

Caregiver Asia Home Allergy Blood Test Services

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