Tuesday, May 19, 2009

"Being Treated as Allergic" vs. "Allergic" (and also: why I'm not convinced Georgia's allergic to eggs)

Okay, this is a subject that is still confusing to me.

Medical testing for food allergies is notoriously inaccurate in that it gives a lot of false positives. So, if someone gets a positive skin or blood test, how do you know if it's an indicator of a true allergy or just a false positive? Well, you rely on whether the person has had a reaction to actually ingesting that food. If so, then you can feel confident that the positive test result is accurate. If not, then there's a very good chance that it was a false positive.

Fine, but what about if the person hasn't ever even tried the food in question? Seems you might just feed it to them to find out if they're allergic, but it's not that simple because that can be quite risky. My understanding is that they (the doctors) look at a couple of factors: (a) the age of the patient, and (b) the numeric result of the RAST (blood) test.

Age of Patient: I could have this wrong, but I think that in some cases, based on the age of the patient alone, the doctors will not proceed with a food challenge or suggest that the child eat the food, because it is safer to just wait and have the patient re-tested in a year. Whether a food challenge may be in order is something that gets considered when the child is a little bit older.

Numeric Result of the RAST test: For whatever reason, each food has a different scale on the RAST test - (this is what I've been told, anyway). So, maybe egg ranges from 0 to 10, but peanut ranges from 0 to 15, and apple ranges from 0 to 12, or something like that. (I am making these numbers up, they may be more like 0-100, but that's not important.) The score on the RAST test is not considered to be an indicator of the severity of the allergy. You could score a 1 for peanut, and so long as it's a true positive and not a false positive, you may have the same allergic reaction to peanuts as someone scoring a 15 on the peanut scale. However, the score on the RAST test is believed to correlate with the degree of reliability of a positive result. So, for instance, if someone scores a 14 on the peanut scale, maybe that means the doctor is 95% certain that that's a true positive rather than a false positive, whereas if someone scores an 8 on the peanut scale the doctor may feel that there's only a 70% chance that that's a true positive. (Again - I am making up the numbers here just to get down the general concept.)

What a mess, right? Because in the end, even though the degree of certainty from the test results varies depending on the person's score, the person who scored an 8 (or a 1 or whatever for that matter) might very well actually be allergic to the food in question.

So, bringing this all back to Georgia....
In her case, she scored just barely high enough on the RAST test for eggs that the doctor did not feel comfortable letting us do a food challenge for eggs. In other words, her numeric score gave the doctor just enough certainty that the positive result was a true positive that she doesn't want to chance a bad reaction by feeding Georgia any eggs. So, we have been instructed to eliminate all eggs from Georgia's diet and are following the doctor's orders on this.

I have my doubts that Georgia is actually allergic to eggs. Maybe that is wrong of me to say, but I am just being honest. I say this because of 3 things: (a) prior to allergy testing, she had previously eaten cooked egg yolks without any observable reaction [granted, it is the protein in the egg whites, not the yolks, that people are allergic to, but given that we had separated these eggs by hand prior to cooking the yolks for her, I somehow doubt we actually removed every single egg white particle perfectly in the process of separating, so she probably ate some, right?], (b) she had birthday cake when she turned 1 without any observable reaction [although, admittedly, there are studies out there showing that some people with egg allergy can tolerate eggs cooked at very high temperatures - like in baked goods], and (c) the fact that her RAST blood test result for egg was just barely high enough for us to miss the cutoff point at which the doctor would've considered her eligible for a food challenge for eggs. So, I could be wrong, obviously, but I'm just being honest and saying that in my heart of hearts I do not think that Georgia is actually allergic to eggs. My hope is that when we go back in the fall of '09 for additional testing that Georgia will test even lower on the RAST test for eggs and will be cleared for a food challenge, and that my doubts of her egg allergy will be proven correct, (or, if she is actually allergic to eggs now that she will have outgrown the allergy). All of this said, we are not idiots and are therefore following the doctor's orders to a T. We do not feed her any eggs. We describe her to others as allergic to eggs and expect them to treat her accordingly - because the doctor has told us that she is - simple as that.

Anyway....getting back to the whole testing thing....
Georgia was not tested for poppy seed allergy when we had her tested for allergies in the fall of '08 (good Lord, why would she be? poppy seeds, for cryin' out loud?!), but several months later she later had a reaction to poppy seeds, so I had to call the allergist about that. During this phone call I asked a few more questions about the testing and got some clarification. My question was basically: "Is Georgia allergic to peanuts? Because I know she tested positive for those, but she has never eaten them, so how do we know?" (i.e., how do we know that these weren't false positive results?)

Answer (paraphrasing here, obviously): She scored an 8.19 on the RAST test for peanuts. At this level, judging only from the RAST results, (since she hasn't eaten any peanuts yet (except via breastmilk) or had any known reaction to peanuts), it is "probable but not certain" that she is allergic to peanuts. Her RAST score does not put her into a category where we could say with above 95% certainty that she is allergic to peanuts. But based on the probability that she is allergic, we are advising you to delay introduction of peanuts to her diet. If, one day, she is able to score below a 5 on the RAST test for peanuts, and she is at that point over 3 years of age, then we will probably do a food challenge for peanuts to find out for sure. Until those criteria have been met, it would be too risky to do a food challenge. (Peanuts being notorious for causing the most severe of reactions, like anaphylaxis, in those who are allergic.)

So, to sum up: since Georgia has never eaten a peanut (except via breastmilk) or had a known reaction to eating a peanut, the allergist might technically say that Georgia is "being treated as allergic" to peanuts rather than saying that she is certain that Georgia "is allergic" to peanuts. But from a practical standpoint, this is a distinction with no meaning. Either way, the point is that she can't eat anything with peanuts. So everyone, including the allergist, would/should just call her "allergic to peanuts" for simplicity's sake until it's been proven otherwise, (which unfortunately, it sounds like we can't even hope for happening until she's at least 3 years old).

EDITED 8/12/09 TO ADD: Since writing this post, I've learned a little bit more about the RAST testing, and I don't think I explained it quite right here. My understanding is that the scale is the same for each food, it's just that for each food there is a different point at which the doctors will say with 95% certainty that you are allergic to that food. So, for instance, a score of 4.5 for shellfish and a score of 4.5 for peanuts may not mean the same thing as far as the chances that each result is a "true" positive. This post from 8/8/09 explains it a little better, I think.

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