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Is A Sweat Test Used For Anything Beyond CF Screening?
14 replies to this topic
Posted 22 February 2012 - 05:48 PM
My son is dealing with encopresis (involuntary soiling). As part of the long line of various professionals we have seen/will be seeing, the specialist paed has recommended a sweat test. Someone from Westmead called me today to book.
When I went online to learn more about what the test would involve, I noted that it seems to be solely as a screen for CF.
I am a bit puzzled, as I was tested before having children (my first cousin has two children with CF, hence the concern). I am not a carrier. I also had a clear amnio with my son, with CF one of the genetic orders tested for via that process.
The paed can be a bit difficult to reach, though I know that I will have to follow up directly with her. Just want to get some input from parents of kids with CF and/or those in the know about sweat tests.
Am I missing something? Does the sweat test have any other purpose?
Thanks for any insights.
Posted 22 February 2012 - 05:53 PM
there are 2 other? very rare conditions that are tested through it. My 2 year old has CF but Dh was tested as a carrier as he has a cousin with it the genetics didnt match at all and we still dont know her genetics for CF.
Posted 22 February 2012 - 06:02 PM
Thanks CF Mummy!
I guess I had to dig a bit harder on the internet (most of the general information just talks about CF).
I see that:
There are other conditions besides CF that can cause positive sweat tests. These include anorexia nervosa, Addisonâ€™s disease, nephrogenic diabetes insipidus, and hypothyroidism. Edema can result in a false negative result.
Interesting stuff. Of course, I am not wanting or expecting anything to come back positive, but I'd like to be as informed as possible.
Posted 22 February 2012 - 06:26 PM
Thats what I was hoping when we got our first positive sweat test that it was nasty joke hope all the tests come back clear
Posted 22 February 2012 - 06:36 PM
Ectodermal dysplasia springs to mind when I hear sweat test I must say. Hope everything comes back OK......errrm, yeah, understatament!!
Posted 22 February 2012 - 06:53 PM
Also I remember reading the BT for checking for CF doesn't test for all stains, just like the heel prick only tests the most common forms of CF. So you can still be a carrier but unable to be tested still. Same with the amnio. Its not 100% still as they find new genetic makeups for it.
I think basically the sweat test is the major test to completely rule out CF. My son had it done at 6 weeks even though his heel prick came back fine because of the reason that the BT doesn't pick them all up and he had some signs that can be CF - since its a pretty non-invasive test its a good one to get done and rule out of conditions it could be.
Hopefully it will be fine and soon you may have a answer for your son.
Posted 23 February 2012 - 04:58 PM
BMJ- CF gene testing only tests for up to 50 (depending on the particular panel used, place of testing, etc.) of the >1000 gene mutations that cause CF. Theoretically, one can be a carrier of a CF gene mutation (or even have CF) and deliver a negative result after an amnio/CVS/Guthrie test. Having said that, the most common mutation (ΔF508) accounts for ~70% of CF gene mutations worldwide, and the five most common gene mutations account for more than 90% of mutations worldwide, so it would be highly unlikely that you are the carrier of a CF gene mutation. This would be especially true if you know which gene mutation(s) your cousin's children carry, and you have tested negative for that particular mutation.
The sweat test, not genetic testing, is the 'gold standard' test in the diagnosis of CF, and with your family history the paed. might want to rule it out absolutely. As I'm sure you know, chronic constipation can be a symptom of CF. I would assume the sweat test- as a diagnostic tool- can be used to test for any condition which alters the composition of sweat, but I'm afraid my expertise in this area starts and ends with CF
Best of luck, and I hope all of the tests return negative results. It must be a stressful time for you all.
Edited because my delta would not cooperate.
Edited by mummasaurus, 23 February 2012 - 05:32 PM.
Posted 23 February 2012 - 05:07 PM
mummasaurus: Thanks so much for that very thorough explanation. I am usually in the position on this board of offering advice/information, as opposed to seeking it. It is good for me to learn something new about CF, especially given that it is in our extended family.
Thanks to all of you, too, for your well wishes. I'll keep you posted on the results!
Posted 23 February 2012 - 05:35 PM
My pleasure; I'm glad my spiel was useful.
If you think I can be helpful in any other way please don't hesitate to PM me
Posted 23 February 2012 - 06:19 PM
I can't really add any more to the explanation of the Sweat test that mummasaurus gave (she nailed it! LOL!)...
From the discussions we had with the Genetic Counsellors (in the context of CF) the Sweat test can identify 90% of the CF mutations but to get a complete analysis done (ie. analysis for 100% of CF mutations) you would have to send your DNA away for genetic mapping (to France if I recall correctly).
However that does not answer your question about what other conditions a Sweat test can test for. Sorry, we have only used it in context of testing our DS's for CF (I am a carrier).
But the real reason for my post is that I just wanted to say that I have often read your posts where you are helping/comforting other people and I just wanted to say good luck to you and your DS with the Sweat test. I hope you get the results quickly and they are all clear.
All the best
Posted 27 March 2012 - 04:02 PM
Thanks for the notes of support and information. What an eye opening experience this has been.
I am happy to report that my son's sweat test came back negative.
I am relieved but also thinking of the other families who were going through testing that same day.
Posted 27 March 2012 - 04:19 PM
BMJ - I'm so glad the tests came back negative. You don't need the extra worry and stress do you. Big hugs to your kids.
Posted 27 March 2012 - 04:21 PM
I was just thinking of you, too. With the issues they've had on EB of people being able to read other members' PMs, I've just deleted a bunch of mine. I just nuked the first exchanges that you & I had. Sad. Oh well, there's always Facebook...
Posted 27 March 2012 - 05:46 PM
I'm so glad your DS is okay. So what's next? Do you keep testing for something else or try to manage the soiling as a condition in itself?
ps Just thinking about you & your two littlies today sitting at the LC waiting room.
Posted 30 March 2012 - 01:00 AM
What great news BMJ, so pleased to hear it Thanks for the update.
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