9/17/2012
Interpretation of positive ara-h2 result with total peanut IgE 0.30 kUA/L - oral challenge or no?

History: 3yo female w h/o peanut reaction

PMH
1 Diffuse "redness" @ birth (?dermatitis) that has 2 since completely resolved
mild dermographism

Event timeline:

1yo- given peanut butter as snack- no reaction

2yo- 2nd exposure in lifetime w peanut butter as snack
Within moments, face became red & blotchy [rash requiring hydrocortisone gradually resolved over 1 week]. 1 parent but not the other parent noted slight wheeze.
Skin test ~1 month after reaction
Peanut 6mm/25mm, almond 2/3mm, walnut 3/4mm, cashew 0/0mm | histamine 6/36mm saline 0/0
Passed almond challenge & eats almonds

3yo- No interval exposure
Skin tests ~1 year after reaction
Peanut 5/15mm, histamine 3/4mm, saline 2/4mm

Ara h2 test result ~1 year after reaction [Uknow kit]
Peanut total 0.30 kUA/L
ara h2 0.21 kUA/L [classified as positive]

I asked another allergist in the practice whether it would be advisable to do an oral challenge to clarify and the answer was "Sure"

I am "on the fence"

What are your thoughts?

Thank you for your inquiry.

As you know, the use of component testing to predict reactivity to food challenge is rather new. There was, however, a fairly recent excellent article dealing with this issue (Dang T, et al. Increasing the accuracy of peanut allergy diagnosis by using Ara h2. J Allergy Clin Immunol 2012; 129:1056-1063). I am going to ask the corresponding author of this study, Dr. Katrina J. Allen, to respond to your inquiry.

As soon as we receive Dr. Allen’s response, we will forward it to you.

Thank you again for your inquiry.

Sincerely,
Phil Lieberman, M.D.

We received a response from Dr. Katrina Allen. Thank you again for your inquiry and we hope this response is helpful to you.
 
Sincerely,
Phil Lieberman, M.D.
 
Response from Dr. Katrina Allen:
In my opinion the combination of a recent ingestion reaction history to peanut and a persistently elevated SPT>8mm would suggest that this patient is highly likely to be peanut allergic (>95% likely) and therefore an oral food challenge is not currently warranted. Based on our algorithm those with a clearly positive SPT greater than the 95% PPV do not need an Arah2 testing undertaken since the SPT is sufficient evidence that allergy is likely.

The one proviso of our results is that they are based on challenges at diagnosis at age 1 years- rather than challenges undertaken in those with persistently elevated SPT or RAST at an older age (as per this patient).

Our Healthnuts cohort is now being followed and serum taken again at age 4 years and 6 years. Data from follow up will help inform the role of Arah2 in diagnosing the development of tolerance in older children.

Kind Regards
Professor Katrina J. Allen, MBBS, BMedSc, FRACP, FAAAAI, PhD
Director, Population Health, Genes and Environment Research Theme
Group Leader Gastro and Food Allergy Research Group
Murdoch Childrens Research Institute
Paediatric Gastroenterologist/Allergist, Department of Allergy, The Royal Children's Hospital
Professorial Fellow, Department of Pediatrics, The University of Melbourne
Charles and Sylvia Viertel Senior Research Fellow
Flemington Road Parkville Victoria 3052 Australia