Is there a positive predictive value for sesame?

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admin rebekahc:
CMdeux
Moderator1
Posted: 08.04.2008 at 03:54:16

I've looked and looked... there doesn't seem to be a published PPV for sesame anywhere.

Based on what other similar type of proteins are, though, I'd hazard a guess that the 90% PPV for any seed-storage protein is probably between 8 kU/L and 14 kU/L via RAST.

"To travel hopefully is a better thing than to arrive." -Robert Louis Stevenson

USA

admin rebekahc:
Posted: 08.05.2008 at 09:44:35

This looks like an interesting study ...

http://www.jacionline.org/article/S0091-6749(08)00729-X/fulltext

Did your son have the challenge today? If so, how did it go?

« Last Edited by 08.05.2008 at 09:54:42 »

admin rebekahc:
CMdeux
Moderator1
Posted: 08.06.2008 at 01:01:20

Excellent!

--- Quote ---We have conducted the first study to evaluate the diagnostic value of sesame-specific IgE. We were unable to establish a threshold, in our population, with a 95% positive predictive value. At a sesame-specific IgE threshold of 7 kUA/L, the positive predictive value was 74.1% and did not increase monotonically at higher thresholds.
--- End quote ---

(So 3 of 4 people with a RAST >7 kU/L are clinically allergic, basically... but the error associated is fairly large.... the only firm statistical conclusion was that if your RAST <0.35 kU/L that you are really, REALLY unlikely to be allergic.)

--- Quote ---Although our study is limited by a small sample of cases, the sample size is similar to that in the study by Sampson5 of wheat and soy IgE, which also did not predict allergy. It is possible that a larger sample would be successful in establishing a threshold. Another potential limitation of our study is that allergy or tolerance to sesame was usually determined by history rather than the gold standard food challenge. Although history is subject to recall and reporting bias, we applied strict inclusion and exclusion criteria. Furthermore, other studies have relied on clinical history to define their allergic cohort.6, 7, 8 The several year delay between convincing reaction and measurement of sesame-specific IgE is also a limitation of our study because it raises the concern that the sesame allergy may have resolved at the time of the IgE measurement.
--- End quote ---

Good points, all. Particularly the portion I've bolded.

Finally, the portion that I think is most relevant to this community (as a whole):

--- Quote ---Further, the clinician should be aware of the potential for patients with peanut allergy to be falsely labeled as having sesame allergy if this diagnosis is solely based on the sesame-specific IgE. We suggest that if a patient clearly tolerates sesame, it is not warranted to obtain a sesame-specific IgE. Alternatively, if the patient's history is truly convincing of a significant allergic reaction to sesame, regardless of the SPT result or sesame-specific IgE level, the patient should be considered allergic, because anaphylaxis to sesame has been described with negative SPT and IgE levels.

--- End quote ---

"To travel hopefully is a better thing than to arrive." -Robert Louis Stevenson

USA

admin rebekahc:
DoubleAs
Member
Posted: 08.06.2008 at 02:44:47

Thanks, KPSesame, for the link. Like CMDeux, I found it very interesting. I guess my son falls into that group of 25% or so who RAST higher than 7 and are not allergic...

We did the challenge yesterday. I was sweating bullets and my son was excited -- go figure. He remembers eating sesame crackers, hummos, and baba ghanoujh and liking these foods. So unlike when we tried to challenge peanuts back in early June and he refused to eat them because they tasted "yucky", he was excited to eat the sesame. They had us bring in a jar of sesame seeds and food to mix them into. We brought a safe bagel and cream cheese and they spread the sesame seeds onto the cream cheese and mashed them in. Then he ate it in increasing amounts over close to 2 hours and then we waited around for another two hours and nothing happened They told us to watch for a skin reaction during the afternoon or evening or into early this morning, just in case. But, according to the allergist this morning, he passed the challenge because he didn't have any skin reactions either.

Only those of you here know how good this feels and how truly relieved I am to "just" worry about nuts and eggs Thanks to all who posted kind words before the challenge.

The allergist said that he was never allergic (remember that he ate sesame regularly until December) -- but with a positive SPT and 22 RAST, it made sense to avoid until we could safely challenge. I asked why his RAST would be so high when he's not allergic and she said that they are seeing this more and more often. She cited one of her patients who had a RAST 30 to wheat and had avoided for years based on testing, but passed an oral challenge last week.

As far as the peanut/sesame connection cited in the article link of KPSesame's, we don't know if my son is allergic to peanut. We have no reaction history (he ate peanut containing foods a few times before being diagnosed with TNA) and a negative SPT. His RAST is .72 (but was <.35 at age 3). He ate 2.5 peanuts when challenged in June and had no reaction, but hated them and refused to continue eating them. We treat him as peanut allergic.

admin rebekahc:
Posted: 08.06.2008 at 03:32:25

Congratulations DoubleAs !!! I'm very happy for you & your son.
Sesame is very potent, so just keep an eye on him when he eats it during the next few months. Congrats again

« Last Edited by 07.11.2010 at 12:42:06 »