IgE Numbers, Part 2

At our visit to Duke this week, I was able to spend some time talking with one of the wonderful nurse practitioners about the upcoming food challenges.  Several of the Peanut Sublingual Immunotherapy participants are quickly approaching the 12 month mark and the first challenges are scheduled for December 10th and the 14th.  I mentioned how I was anxiously awaiting the results, and she very quickly reeled me back in. With this being the first peanut sublingual study for children, there are a lot of unknowns.  It's very possible that the first food challenge won't show significant results and may even mean a change to the study protocol.  I'll still call soon after the challenges to find out the results, and hopefully, the kids consume the equivalent of a peanut or two.  If they don't, then we'll keep pushing through, Abigail will keep taking her drops and we'll hope that with more time we'll all see the results we are hoping for.

I'd love to be able to see Abigail's IgE numbers over the course of the study, but they are sealed until the end.  The goal is to get her number down from 14 to a single digit.  At a single digit, her chance of having a allergic reaction drops significantly, as well as the risk of anaphylaxis.  She'd still be allergic to peanuts, but her allergy would not be life threatening.  Abigail would be considered "cured" of her peanut allergy if her number was a 1 or less.  She's had two blood draws to determine her IgE number since starting the study.  The first was the baseline (which was 14), and then again at 4 months.  Her next blood draw is at the 8 month mark.  We can't see the numbers so that we don't get discouraged if they're not changing.

IgE numbers only tell the percentage chance of having an allergic reaction, they do not tell the type of reaction or severity.  Whether the IgE number is 14 or 364, there is still a 95% chance of having a reaction.  I'm going from memory (which is often a risky proposition), but I seem to recall that when Abigail was tested at age 2 and scored a 12, she had something like an 80% chance of having an allergic reaction.  In fact, the doctors at Duke are seeing a trend that their patients with lower IgE numbers are having more severe reactions than those with really high IgE levels.

So, there is a possibility that Abigail's score of 14 might mean that she would have a more severe reaction than a child having a score of 364.  I do feel that she has an advantage starting the study with a lower number. Doesn't it stand to reason that the lower the number, the less distance one has to go to get to single digits? Maybe it takes less time to build up a tolerance to peanuts with the sublingual therapy?

Here's a table that I copied from Wikipedia that shows IgE levels and their correlating allergen scores using the RAST test method.

RAST rating	IgE level (KU/L)	comment
0	< 0.35	ABSENT OR UNDETECTABLE ALLERGEN SPECIFIC IgE
1	0.35 - 0.69	LOW OF ALLERGEN SPECIFIC IgE
2	0.70 - 3.49	MODERATE LEVEL OF ALLERGEN SPECIFIC IgE
3	3.50 - 17.49	HIGH LEVEL OF ALLERGEN SPECIFIC IgE
4	17.50 - 49.99	VERY HIGH LEVEL OF ALLERGEN SPECIFIC IgE
5	50.0 - 100.00	VERY HIGH LEVEL OF ALLERGEN SPECIFIC IgE
6	> 100.00	EXTREMELY HIGH LEVEL OF ALLERGEN SPECIFIC IgE

Here are a couple of other things I learned from our many trips to Duke.  First, if a child doesn't outgrow a peanut allergy by the age of 5, he or she usually won't.  Second, IgE blood tests are not standardized.  The RAST test was primarily used from 1974, when it was invented, until 1989, when it was replaced by the ImmunoCap Specific IgE blood test.  This test may also be described as CAP RAST, CAP FEIA or Pharmacia CAP.  Wikipedia states that approximately 80% of the world's commercial clinical labs are using this newer version.  But, if you are comparing recent IgE blood test results to a previous test, you need to make sure that the labs are using the same test method.  Because the "Class" scale is assigned by the lab, unless you are comparing results using the same test method, one person's Class 3 may not be the same as someone elses.

We've got just one more visit before Abigail is on the "Maintenance Dose."  That means some relief for us on the frequency of trips.  After this next visit, we don't go again for six weeks.   Just in time for the holidays!