Author Topic: Allergy Testing: blood testing vs. scratch test?  (Read 5801 times)

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Offline Austin's mom

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Allergy Testing: blood testing vs. scratch test?
« on: April 11, 2010, 03:16:03 am »
I took austin to the Allergist this week. He tested neg to milk and soy, which didn't make sense to me, because I know for a fact he at least has an intolerance to both. (He was projectile vomiting and was covered in horrible eczema rashes until he went off).

 I was super confused until I read yesterday that there are 3 types of reactions people can have. The first, is the immediate, with in 15 minutes. The second up to 20 hours, and the third, delayed, after 20 hours.

Well the allergist didn't even bother to ask me which group he feel into. He always reacts the following day 20+ hours later. If its food, detergent, diapers etc. (Which makes it really challenging to figure out what the reaction was to).

What this article said is that the group of children in the third group, the delayed reaction, only 1 out of 5 respond positively to the scratch test.

I just can't believe they didn't ask when I noticed the reaction, and did not do a blood test. Even his pead said that they should do a RAST test (which is the blood, i thinki?) Has anyone else had experience where the scratch test came out neg and the blood positive?

Offline birdie

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #1 on: April 11, 2010, 05:20:03 am »
Has Austin been M/S free for awhile?? If so, that might explain the negative test results as the tests look for antibodies created in response to an allergan exposure.  There are also different types of blood allergy tests that can be done...one is a more of a long term view.  When we were fighting this battle, our pediatirician would not send us for allergy testing.  DS has the delayed reaction and I just wanted to know what to avoid.  But she said the results of allergy testing are not reliable until the age of 3.  But I have heard others say different.  I also spoke to a nautropath who was willing to do some testing but she was suggesting a different type of blood test than pediatrician.

Sorry not much help. Good luck!!
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Offline MasynSpencerElliotte

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #2 on: April 11, 2010, 05:33:43 am »
We just did scratch & blood tests and they both showed negative (for milk & eggs)...but she has not eaten eggs in 7 months and milk for about 3. I think the milk thing is an intolerance though, not a true allergy. So, on the allergists advice I fed her a 1/4 of a cookie from a recipe made with one egg. She turned very red (like a patchy sunburn) and got a bit of a runny nose (but we have had colds lately too).  Now I am waiting until Mon to phone them and see how to proceed.

Wendy, our GP wouldn't send Spencer for testing either, we had to go to another doctor for that. Our GP wanted to wait until she had a full blown anaphylactic reaction to do anything!
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Offline Mashi

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #3 on: April 11, 2010, 07:11:03 am »
Allergies and intolerances are different.  I suspect your DS has an intolerance to milk and not an allergy, and as alergists deal with allergies and not disgestive system issues it's not in your allergist's area of expertise to diagnose a milk intolerance.

An allergy to milk (or to anything) will trigger an immune system reaction - the body recognises the substance as "foreign" and reacts to that in different ways - most common are skin reactions such as hives, eczema, watery eyes, runny nose, and for some people anaphylactic shock, though there are other reactions possible. A blood test is looking for an IgE reaction which is an immune system reaction.  An allergic reaction tends to be quite immediate.

An intolerance to milk (or any other food) happens in the digestive system - usually the intestines, when they start to break down the food and process it.  When the intestine can not properly tolerate and break down the food (in the case of milk it is the protein) then the common reactions are cramps, vomiting, diarrhea or constipation, and prolonged exposure to the substance causes skin reactions in many people.  Symptoms of an intolerance tend to be delayed and not immediate, as it takes the time for the food to travel through the digestive system, the body to try to deal with it and then not be able to.

So your allergist testing for an allergic (immune system) reaction is doing just that, and not looking at the digestive system, which is not what his area of study is and so he would not.  This is why they say that testing for food allergies is not always accurate - if you get a positive result then it is positive, but a negative result does not mean there are no known issues with the food.

My own paed (hospital paed GI consultant) refused to test for food problems because of this, except in extreme cases.  Diagnosis for milk allergy was clinical - meaning the child is having problems and these symptoms, so we remove milk and if the symptoms clear up then it's a positive diagnosis.  He was also VERY keen on stressing that an intolerance is no less serious than an allergy and that the two terms are often used interchangeably because the end result is the same...NO MILK.  He personally even preferred to just use the term allergy with parents because many people mistakenly believe that an intolerance means that if you keep exposing the child to it that they will then build up tolerance, which is wrong. However, once you say "allergy"  people are usually quick to avoid it at all costs.   So when you say he has "at least" an intolerance to milk and soy, it should not be seen as something less serious than an allergy - he's got an intolerance and needs to avoid milk and soy 100% just as if it was an allergy.

Exposure to the substance that you are allergic to can make the immune system reaction stronger and stronger each time, and be VERY uncomfortable for children and can be dangerous. Continued exposure to foods you are intolerance to can continually cause more and more damage to the digestive system, more pain, more symptoms and so on.

I am not 100% sure on this part, but when you ask about the scratch test versus the blood test, I believe that the blood test will show an IgE "marker" for the substance, meaning that the body is saying that it sees this as a foreign substance, but then when that substance enters the body it is not necessarily triggering a reaction. A scratch test is just looking at reactions that occur. Again, means that the substance should still be avoided if it shows up on the blood test, as just because there is no reaction at the moment doesn't mean there won't be one in the future.

Hope some of this is helpful!

Offline MLK

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #4 on: April 11, 2010, 08:59:37 am »
My kid's paed also said that testing for allergy/intolerance in kids under 3 was best done by elimination for 2-3 weeks then challenge, a couple of times if necessary. If there is a serious rection the challenge needs to be in doc's offices or hospital.

Offline Katet

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #5 on: April 11, 2010, 09:21:00 am »
I worked in Immunology research for 10 years so have a reasonable understanding.

Intolerance to Milk is very different to an allergy, vomiting is more often a sign of intolerance & as the PP said, an allergy is generally a pretty rapid reaction, in non medical circles the terms tend to be used a bit interchangably, but an allergy has an IgE response.

My DS1 (6.5) was tested (RAST) at 6 for allergies, he had an IgE response to shellfish, but as a baby he had (cows) milk intolerance & would throw up about 5 hours after milk (was ok with BF) ... he came back negative for cows milk. That totally makes sense to me, he can tolerate about 1 cup of milk/day no problem, but 2 serves & his sneezing etc gets worse, if he was allergic, he wouldn't be able to have any... but as babies only have milk they have nothing to "buffer" the milk that gives the problem, but generally can cope when they are older & milk is a much smaller part of their diet (& often the part that causes the intolerance isn't an issue with processed dairy such as cheese.

The thing is a rash from say diapers/detergent, doesn't have to be an allergy (ie IgE response) it can just be a skin reaction due to a sensitivity... eg  I am sensitive to certain sunscreens because they react with my skin (sweat), but I don't produce IgE to it.

Mashi, not quite right on blood v skin, both measure the IgE levels to a specific antigen (eg antigens in milk). The differences are that there are less "antigens" that can be tested by the RAST (blood), it is more expensive & it takes much longer to get results & there are potentially more issues from collecting blood, esp in young children... the volume needed from a baby is pretty big in relationship to a baby's size.

So I'm thinking in terms of the OP (as it very often the case with a 4mo), it is an intolerance... infact I'm really surprised that a 4mo was tested for allergies, as it is far more common for a child under 1 to be MSPI than allergic.

As the PP said an intolerance to food can be just as dangerous as an allergy, but it won't show an IgE response. Both do have the potential to be "outgrown" if the body isn't exposed to them for a period of time (particularly with children)... although in the case of intolerance it is generally that the body can cope with a certain amount, but more will cause an issue, with an allergy, the body no longer reacts, so any amount is ok.
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Offline Mashi

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #6 on: April 11, 2010, 09:24:21 am »
Mashi, not quite right on blood v skin, both measure the IgE levels to a specific antigen (eg antigens in milk). The differences are that there are less "antigens" that can be tested by the RAST (blood), it is more expensive & it takes much longer to get results & there are potentially more issues from collecting blood, esp in young children... the volume needed from a baby is pretty big in relationship to a baby's size.

Thanks for correcting Kate, wasn't 100% on it but am always interested in this area of medicine so now I have learned something new!!

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #7 on: April 11, 2010, 17:53:26 pm »
Great information Kate and Mashi - thanks...I'm learning new stuff too!   ;D

...back later....

Offline pamelamcgahon

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #8 on: April 11, 2010, 19:49:13 pm »
Wow, thanks for the info guys.  My GI said we weren't to test Keira for allergies etc and just to eliminate and re challenge the cows milk as tests weren't reliable.  Her symptoms were tummy pain - crying all the time from it - and making grunting and groaning noises constantly, both stopped on hydrolysed milk.  She also had exzema on cows milk.  She sounded constipated but had 4 or 5 dirty nappies a day!  Soya milk did the opposite, complete runny nappies, stinking, screaming as her bum was burning!  GI said MSP allergy though and to eliminate til 12 months both.  She said not lactose intolerance as soya would have sorted it out.  Referred to dietician now who was really surprised with both our GP and GI's way of dealing with the whole thing (too long to go into, reflux was also in the equation).

Thanks again
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Offline Austin's mom

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #9 on: April 11, 2010, 22:28:00 pm »
You all are sooo helpful! I understand so much better now. Thank you! The allergist did say to stay off milk/soy for 12 more weeks, (he has been off completely about 3-4) and then try milk again. I guess that is the challenge  you were talking about.

So in your opinions then- with all the information you just provided, if his eczema continues to get worse, and cover more parts of his body, (it has now spread to his back) Do you think that is a result of the intolerance, or just a coincidence? It started on small patches on his face,by his eyes and scalp, and has spread to his whole chest, belly and now his back. He also has a rash on the back of his neck and cheeks and behind his ears. Thankfully the diaper rash just cleared when i switched to hypo diapers. I just don't know how to tell anymore.

Offline Katet

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Re: Allergy Testing: blood testing vs. scratch test?
« Reply #10 on: April 11, 2010, 22:50:03 pm »
Eczema is in many ways a "stress" response to something that the body is exeriencing, so it can be linked to allergy & intolerance. But it may also be something unrelated that his skin comes in contact with. Do you use hand creams, perfumes etc, they could actually be causing it by skin to skin contact.
 Has a medical professional recommended anything you can use for it. I know my friend whose DD has it doesn't wash her DD with soap, but uses sorbeline cream. I'd be having a good chat with the GP about how to treat the eczema & even get a referal to a dermatolgist in case it actually isn't eczema (which was the case with my DS1)
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