Skin Prick Testing

Skin prick testing is a way of diagnosing IgE mediated allergies. There is no absolute result and the testing must take into account what actually happens to the child with different allergens.

Ads

What is a skin prick test (SPT)?

SPTs are a way of testing for allergies that are IgE mediated - to read more about IgE mediated reactions, click here.

The test is looking for evidence of a reaction to a certain substance (usually a food) when it is put in the skin.

Back to list

Advertisement

How are skin prick tests performed?

Usually, the skin tests are done on the forearm or the back in small children. Once a decision has been made what is to be tested, small drops of fluid containing the test material are put on the skin. Then a lancet is used to prick the skin through the fluid. After 10-15 minutes, the size of the reaction is noted.

Back to list

Does it hurt?

SPT does not really hurt. At most it might be a little uncomfortable - like a scratch. The skin is hardly broken by the lancet.

Back to list

Does a positive skin prick test mean my child has allergy?

Not necessarily. The skin may react but your child may have no reaction at all when eating that food. The larger the reaction, the more likely it is there will be an actual allergic reaction to that substance.

For that reason, it is important to test only substances that you think your child may be allergic to rather than test everything.

To be sure, your doctor may want to do a formal food challenge in hospital to confirm the allergy. This is when your child is given the food in a safe environment so it there is any reaction, no harm will come to your child.

Back to list

What size skin reaction is likely to be associated with an actual allergic reaction?

It depends on the age of the child and there is no absolute size, but the following test results were all associated with a positive food challenge.

The wheal size refers to the size of the swollen area of skin. It may have some redness around it but don't measure that.

Wheal
Less than 2 years of age
More than 2 years of age
Milk
 6 mm or more
  8 mm or more
Egg
 5 mm or more
 7 mm or more
Peanut
 4 mm or more
 8 mm or more

Back to list

Advertisement

Are skin prick tests better than blood tests for allergy?

The SPT and the RAST (or EAST) blood tests give similar information. The higher the blood test result the more likely an actual reaction, just like the skin test. The advantage of the SPT is that you get an immediate result.

However, you can't test on skin that is covered with eczema so in those cases, the blood test may be better. The blood test may also be better if there have been severe reactions to food, such as peanut, in the past.

Back to list

Are there any precautions for SPTs?

Your child should not be taking anti-histamines - they should be stopped at least 5 days before the test. Some medicines need to be stopped for even longer. Check with your doctor.

Back to list


References

  • Sporik R, Hill DJ, Hosking CS. Specificity of allergen skin prick testing in predicting positive open food challenges to milk, egg and peanut in children. Clin Exp Allergy 2000; 30: 1540-1546.

To go to the top of the Skin Prick Testing page, click here

To go to the main Allergy page, click here

To go to the Food Allergies page, click here

To return to the Home page, click here


Last reviewed 16 May 2011

We comply with the HONcode standard for trustworthy health
information:
verify here.

Dr Maud MD

Dr Maud MD (MBChB, FRACP, FRCPCH), a specialist pediatrician, provides health information and medical advice for parents of babies and toddlers. Read more about Dr Maud.



Special Offer
A must have for new parents

Baby sleep

Essential Baby Sleep
By Dr Maud


We're so excited to announce our first Children Book

The Special and Talented Dog Show
To order click here

The second book published is called

Flying Things

This is aimed at a pre-school audience and is a rhyming story.  You can buy by clicking here

To read more about our children's books, click here



We comply with the HONcode standard for trustworthy health information: verify here.


Visitors Say

Thanks for your "straight to the point" advice! I am very happy that you decided to add your wisdom to the internet for all to read. You made a very worrisome toddler's fever day into something a lot calmer.
Fred, Sweden

Excellent website. Plain english - reassuring and direct. Great resource - thank you.
David, Australia

Dear Dr.Maud, I had to write a thank you note for all the work you put into this site to make our life easier! We had many questions and worries but we found all the answers here very easily. You helped us to find a way to make our little boy eat again and calmed our worried minds when he was sick.. So much useful information, I recommend your website to all moms and dads I know. Thank you so much, you are fantastic! Have a wonderful day! :)
Sophie, Singapore

Thank you so much. I have taken ... to three different Dr.'s and you are the first to answer my questions in a manner that I can understand. You explained everything in English for once, and told me things that none of the other Dr.'s did. Thank you again. I really appreciate your help.
Machelle, United States