Allergy testing siblings

Although my 2 1/2 -year-old son, D, has a life threatening peanut allergy, my daughter C (now 10-months-old) has no known allergies as yet. After D’s anaphylactic reaction to peanuts, the hospital doctors told us that:

  • C would be allergy tested for peanuts and other nuts when she was 3-4 years old.
  • Until she was allergy tested, she too should avoid peanuts and all other nuts.

However, when we attended hospital for D’s skin prick tests in October 2012, the doctor informed us that the policy had changed. C would now NOT be offered allergy testing.

I wasn’t sure what to make of this U-turn, so I decided to look into the likelihood of C also being severely allergic to peanuts.

Do siblings of food allergic children have a higher peanut allergy risk?

So, what is C’s risk?

NHS advice for parents states that a child has a “higher risk” of developing peanut allergy if:

  • S/he has a known allergy (such as eczema or a food allergy); or
  • Their immediate family (parents or siblings) have a food allergy or other allergic condition, such as hay fever, asthma or eczema.

So far, C has shown no signs of having eczema, asthma or other allergies. However, D’s allergic conditions (peanut allergy, eczema and asthma) put her in the “higher risk” bracket.

How high is the “higher risk”?

A 2008 study (by J J Liem and others) concluded that:

“… the sibling of a peanut-allergic child has a dramatically increased risk of developing peanut allergy. This risk is nearly 7-fold greater than those who do not have a sibling with peanut allergy, with an almost 12-fold increased risk for peanut allergy among younger siblings.”

Dr Andrew Clark (a paediatric allergy consultant at Addenbrooke’s Hospital, Cambridge) did a fantastically informative Q&A piece for Mumsnet in April 2010. In this, he confirmed that siblings have a 7% chance of developing nut allergy, compared to a 1-2% background population rate.

If the sibling is allergy tested, what happens next?

If the sibling’s skin prick test results were:

  • Negative, Dr Clark stated there would be a 95% chance that the sibling, who had never eaten peanut, would not react to eating it for the first time. Therefore, there would still be a chance that, even though the test result was negative, the sibling could have a reaction further down the line, once they have eaten it a few times. Following a negative result, the child’s doctors would then advise on how to introduce peanuts.
  • Positive, the doctors would then need to do an “oral food challenge”. Even with a positive skin prick test, the child may be able to eat peanut without having a reaction. It may be that the child (with the positive test result) is sensitised, but not “truly allergic”. The oral food challenge procedure is discussed on the Allergy UK website. Basically, the child would be given the potentially allergenic food in a hospital, under controlled conditions, in case an anaphylactic reaction occurred. Dr Clark noted that the challenge procedure is “time-consuming [and] … not without risk”.

Is sibling allergy testing available on the NHS?

The answer to this seems unclear. There appears to be a general reluctance to allergy test until someone has had an adverse reaction to a food. As regards siblings, Dr Clark acknowledged that the tendency is to delay sibling allergy testing until a child approaches school age, so as not to swamp the allergy service.

Can you go private for allergy testing?

Yes. However, Allergy UK warns of the importance of finding a reputable, trained allergy specialist and has an online search tool for finding a private doctor: see

Unfortunately for us, at the moment, a search within a 50 mile radius of Macclesfield yields no results!

So what are we going to do?

After what happened to D, we would definitely like C to be tested. Until she is, we will make sure she avoids peanut and all other nuts. Luckily, this won’t mean a huge lifestyle change for us, as we are already living nut free because of D’s allergy. Fingers crossed, by the time C reaches 3-4 years of age, the NHS policy will favour testing siblings of peanut allergic children, even if they themselves haven’t yet displayed any allergy symptoms. If not, hopefully we will then be able to find a reputable private allergy specialist local to us.

Update (January 2014): My daughter has now skin prick tested negative for peanut. Here’s what happened as regards the GP referral and what happens next: Allergy testing siblings: quick update.

Update (April 2014): I’m very pleased to report that my daughter passed her peanut challenge and so has avoided having a peanut allergy like her big brother. See How peanut butter found its way back on my shopping list.



  1. Hi

    Really pleased to have found your blog as hearing of others experiences and anxieties. My daughter’s allergy doctor advised that he would not test her (twin -non identical) sister as skin prick testing can give false negative results if the child hasn’t eaten peanuts (or tree nuts) before. We were left to it, in the sense of whether or not to give our other daughter peanuts/nuts, however she has not been willing to try anything and we have not been over keen on it either. Will have to face it at some point as it is better to know if you have a severe allergy? The time just never seems right……

    1. Hi Liz – thanks for your comment! Now my daughter has started nursery, I’m even more keen to have her tested – so she can have her own emergency medication if need be. One of my concerns was, if she tested negative, whether she would have to eat peanut regularly to maintain a tolerance to it (and how much of a headache that would be to arrange, given we need to keep our home nut free for our son). However, I gather eating peanut regularly MIGHT not be necessary. I’m planning to talk to our allergy doctors about all this again at my son’s next appointment – will keep you posted! Louise

  2. Hi again

    Thanks – I look forward to your update. It’s very difficult to keep track on current theories and practice; experience says that it would be preferable to know and be equipped for a reaction, however the doctors seem unable to offer any help. I did ask once at school if they would act if my other daughter had a reaction, and the answer was that they would ring me. My daughter only has three more years of skin prick testing; as far as I know, currently it is provided up until the age of 12. This does, however, give me the chance to look out for developments and if anything becomes available I can make further enquiries. Liz

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