Sweat Test for CF

[anonymous]

Is it true that you can get a false negative on a sweat test.

Grateful for any advice.

Charlotte<img src="i/expressions/face-icon-small-confused.gif" border="0">

 

[miesl]

Yes. There are many reasons to get a false negative. Many of the genetically diagnosed CFers on this site have had negative sweat tests.

 

[anonymous]

My eldest daughter had a sweat test even though she had been medically screened as negative for CF. She had a sweat test done because her younger sister was diagnosed with CF. The test came back negative.

Charlotte<img src="i/expressions/face-icon-small-confused.gif" border="0">

 

[thelizardqueen]

You can get a false negative, but never a false positive. That's why a DNA test is a great idea after you've tried a sweat test.

 

[anonymous]

Actually, you CAN get a false positive on a sweat test, it's just much less likely than a false negative AND it only happens with a small set of diseases. Here's a link that details what disease can cause a false positive:

<a target=_blank class=ftalternatingbarlinklarge href="http://www.labtestsonline.org/understanding/analytes/sweat_chloride/test.html
">http://www.labtestsonline.org/...at_chloride/test.html
</a>Here's an excerpt from it
"Is there anything else I should know?
The sweat test will not pick up carriers of cystic fibrosis. It takes two mutated copies of the CFTR gene to cause cystic fibrosis. Those who are only carriers do not have CF and will not have sweat chloride abnormalities.
<u>There are other conditions besides CF that can cause positive sweat tests. These include anorexia nervosa, Addison's disease, nephrogenic diabetes insipidus, and hypothyroidism. Edema can result in false negatives.</u>

The sweat chloride test should only be performed at specialized centers with experience with this kind of testing. Otherwise, problems in accuracy, including false negatives due to poor collection technique, can arise."

Charlotte, if you're concerned and you know which mutations your dd with cf has, request your dr do a genetic test to screen for the mutations your other dd carries. It's usually much quicker and possibly less expensive when they know which genes to test for.

 

[JazzysMom]

<div class="FTQUOTE"><begin quote><i>Originally posted by: <b>anonymous</b></i>

Actually, you CAN get a false positive on a sweat test, it's just much less likely than a false negative AND it only happens with a small set of diseases. Here's a link that details what disease can cause a false positive:



<a target=_blank class=ftalternatingbarlinklarge href="http://www.labtestsonline.org/understanding/analytes/sweat_chloride/test.html
">http://www.labtestsonline.org/...oride/test.html
</a>
Here's an excerpt from it

"Is there anything else I should know?

The sweat test will not pick up carriers of cystic fibrosis. It takes two mutated copies of the CFTR gene to cause cystic fibrosis. Those who are only carriers do not have CF and will not have sweat chloride abnormalities.

<u>There are other conditions besides CF that can cause positive sweat tests. These include anorexia nervosa, Addison's disease, nephrogenic diabetes insipidus, and hypothyroidism. Edema can result in false negatives.</u>



The sweat chloride test should only be performed at specialized centers with experience with this kind of testing. Otherwise, problems in accuracy, including false negatives due to poor collection technique, can arise."



Charlotte, if you're concerned and you know which mutations your dd with cf has, request your dr do a genetic test to screen for the mutations your other dd carries. It's usually much quicker and possibly less expensive when they know which genes to test for.</end quote></div>


I read this link & thank you for it, but my understanding from it is this. There still is no chance of a false POSITIVE. However; the positive does not have to mean CF. Other health issues can cause this also thus the CF gene mutation panel needs to be done to determine if CF is the reason for the Positive sweat test.