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!

What's an IgE? An Introduction....

I've been wanting to post about IgE numbers for a while, but it involves science and medicine, neither particularly strong subjects for me.  I'm on the opposite end of the spectrum with interests centering around art and design and creative thinking.  So, why even tackle the subject?  Unfortunately, it just keeps coming up.

In conversations, parents of allergic children almost always get around to telling each other what their child's IgE number and/or Class is.  It's pretty much the only definitive description we can say about an otherwise very uncertain physical condition.  My daughter is allergic to peanuts.  Her IgE number is 14.10 kU/L, and she is a Class 3.  The number is up from the last time we had her tested when she was 4.  It does not mean that she is becoming "more allergic".  Her IgE number only tells the likelihood of her having a reaction.  At a 14, I know she has a 95% chance of having a reaction if she ingests any peanut protein.  What I don't know is when or if she'll have a reaction or to what degree of severity.  I don't know if the reaction will only need an antihistamine or require the dreaded EpiPen.  I don't even know how she got her allergy or if she'll have it her entire life.  That IgE number is the only known in a very scary world of unknowns.  We parents hold onto that number.  But what is it really?

There are 3 ways to determine if someone has an allergy.  The most definitive, most expensive and most risky is a food challenge.  The patient starts with a tiny amount of food and continues to ingest until the first sign of a reaction.  If there is a reaction, then the person is allergic.  If not, they're not allergic.  Usually the amount of food is so small that a patient might just break out in hives or maybe vomit, but there is the risk of  anaphylaxis.  At Duke, whenever a food challenge is administered (at least in the clinical trials) an IV is inserted as a precaution.  Abigail is not scheduled for a food challenge until spring of 2010.

Another allergy test method is a skin prick test.  In this test, the skin is pricked and the allergen in question is applied.  If there is an allergy, the prick area swells and the skin around it gets red and itchy (almost like a mosquito bite). The test can be used for both environmental and food allergens.  While this test is uncomfortable and somewhat subjective, it is less expensive and more reliable than the next method which is the blood test.  About.com does a good job describing and comparing both of these tests in layman's terms.  According to the site, blood tests are becoming more useful in determining food allergies because they measure the specific amount of allergic antibody to a food.  The downside of blood tests, however, is they tend to give more false positives and negatives, and may indicate an elevated antibody, i.e., an allergy, which may or may not necessarily equate to an allergic reaction.  It's from the blood test that the IgE numbers and Classes are assigned. 

Blood Test (RAST, CAP-FEIA, ImmunoCAP)

The RAST test or radioallergosorbent test detects the amount of IgE that reacts specifically with a suspected or known allergen (Wikipedia).  It's an older test and many labs are using a non-radio active test like the CAP-FEIA or ImmunoCAP.  Duke University Medical Center uses the CAP-FEIA.  It's important that you know which test your doctor is using, but I'll get to that later.

So what is an IgE?  I'm using a definition from kidshealth.org for Immunoglobulin E (IgE).  It's the simplest definition I can find online.  "IgE is a type of protein in the body called an antibody. As part of the immune system, it plays a role in allergic reactions. When a person is allergic to a particular substance, such as a food or dust, the immune system mistakenly believes that this usually harmless substance is actually harmful to the body. In an attempt to protect the body, IgE is produced by the immune system to fight that particular substance. This starts a chain of events leading to allergy symptoms."  For example, airway constriction in asthma, local inflammation in eczema, increased mucus secretion in allergic rhinitis and potentially fatal drop in blood pressure as in anaphylaxis (again from Wikipedia).   However, perhaps our nurse last week at Duke explained it best.  As she described it to Abigail....the peanut soldiers think they need to fight peanuts but we're training them not to.

In a discussion with Dr. Kim at our last visit to Duke, I learned how the IgE number is determined.  Peanut protein is adhered to the inside of a test tube.  The patient's blood is then poured into the tube, left to sit for a controlled amount of time and then shaken.  The peanut antibodies in the blood will stick to the peanut protein.  In other words, the antibodies in the blood "attack" the protein in the tube much like it does in the patient's body.  The extra blood is then washed off and the blood that is attached to the protein is measured.  That amount is the IgE number.  The Class is something assigned by the particular lab running the sample.

I've found a RAST scale that I want to post.  I also want to discuss a warning about how the big laboratories use different standards when reading the results.  There's also more on the topic about what the IgE numbers actually mean, i.e., chance of out-growing the allergy and chance of having a reaction.  But, I can just picture eyes glazing over with the amount of information thus far.  So, until next time....