False Negative Sweat Tests?

[Inkabinka]

Hi, This is my first post. My 5 yr old daughter, although very vibrant, has had a history of random symptoms her entire life: Asthma, pneumonia (hospitalized 2 times), staph infections, constipation, chronic sinus infections/stuffiness, hyperactivity (I attribute this to her asthma medication). She has always been behind in growth, even in utero. Recently, blood tests showed she has iron deficient anemia and low sodium. She had a negative Sweat Chloride test about two years ago, but unfortunately, I don't know the number - when I asked, I was told that the test is in either in the positive or negative range and that there is no "grey area". She also tested negative for Celiac Disease. I know her pediatrician is concerned about her - she is quick to test every time a new symptom appears. (Typically, her first comment is "We've tested for CF, right?" ) Is it really possible to have a mild case of CF that doesn't test positive with the Sweat Chloride test? Do these symptoms sound like CF? Should I be pushing for genetic testing? Any advice would be appreciated!

Erika

 

[Transplantmommy]

It is more common than some might think to have a negative result and the child actually does have CF. It could even be that they didn't collect enough sweat so the test would not be read properly. It happened to me. Granted I was much younger (3 months old) when I was tested, but I continued to have the symptoms and was tested again at 6 months old, and it was positive.

I would say that if you really want to be sure, get the genetic testing. Does your family have a history of CF? Have you and the father been tested for the gene? These are just common things that you should also be looking at. I hope that you can get things figured out. Good luck.

 

[Ratatosk]

There are several individuals who passed the sweat test with flying colors and genetic tests later showed they did in fact have CF. DS passed his with a normal 32 as a baby; however, his genetic testing showed CF. Check Alyssa's blog about her children's diagnoses.

I just read an article indicating there are 1601 identified mutations for CF. Carrier screening only looks at 30-90 of the most common.

Oh and as far as family history... Both DH and my families have extensive geneology records. No family history.

 

[Mommafirst]

Push for FULL (Ambry amplified) genetic testing. CF comes in lots of different packaging. My daughter had a sweat test that was most certainly in the "grey area" as they put it. Anyone knowledgeable in CF testing would know that there is a 20-30 point range which is considered borderline or inconclusive and is an uncertainty between positive and negative requiring additional testing. I'm guessing that whomever told you that doesn't know as much as they think they do.

Sweat tests are not always performed correctly. You need to have her tested at an accredited CF center (see CFF.org and look for care centers) using an affiliated CF lab.

I hope its not CF, but it certainly would give you answers and a direction.

 

[missnth]

there is no grey area if the test is done correctly. but how do you know if it was done correctly? i would go for more testing, either a repeat of the sweat test or full genetic testing. with symptoms like that you want to know if it's cf or not. because if it is, you want to do something about it. and if it's not, you want to figure out what it is.

 

[CFHockeyMom]

Sweat tests results in the 40-60 range are often considered the "gray area". However, as has been stated, there are many folks on here with "normal" sweat test numbers that later recieved a genetic diagnosis.

False negatives with the sweat test are quite common. Make sure your test was done at an accredited CF center and follow your instincts. Push your ped for a full genetic panel.

 

[JORDYSMOM]

Welcome! I'm sorry you are going through this with your child. We have a lot of people here who had negative or borderline sweat tests, and then found two CF mutations with the genetic testing. I'd recommend getting the full panel test. As Liza stated, there are now over 1600 known mutations, so get the panel that checks for all of them. As others have mentioned, find an accredited CF clinic in your area. I hope you find what you need to help your child. Keep us posted.

Stacey

 

[Inkabinka]

Thanks for all of the feedback! There is no family history of CF, although I also have asthma and have a history of lung infections. I hope it's not CF, but it would be good to have a definite answer so we know how to treat. I will push for another Sweat test and genetic testing to get a definite answer! Thanks!

 

[letefk]

My girls had the same profile as your daughter, and when we did the sweat test, one passed (11) and one was borderline (49). A full Ambry genetic test (you want the FULL Ambry) showed they BOTH had atypical CF. The genetic results were identical in both girls. Yet if my older child had not sweat tested at 49, the younger would not have been tested further.

There have been major shifts in the understanding of the complexity of how the genetics of this disease work; we now know, for instance, that carriers with the right modifier genes can express 'mild', CF-related symptoms. Some kids, like my girls, have only one CF gene, but because of a copying error on the "good" gene, they develop atypical forms of CF.

Many pediatricians are not up to date on the new thinking about CF diagnosis; have you taken her to see a pediatric pulmunologist? If you can find someone who does both asthma and CF care,or works in a clinic were they also treat CF, you might be able to ask them if your daughter's profile would merit an Ambry. That was what we did. She did not work with CF patients, but she consulted with the colleague in the practice that did, and he insisted that we get the genetic test.

I hope you find your answers.

 

[Alyssa]

<b>Whoever told you there is no gray area is wrong</b> - there not only is a gray area (borderline is what it is referred to when test results are between 40-60) but there are many many cases out there of people with clearly normal numbers but yet have two CF genes and a confirmed case of CF.

<b>Yes, her symptoms sound like CF symptoms.</b>

<b>Yes, it is possible to have a mild case</b> (at this time) the symptoms you have mentioned are some of the same symptoms that many with CF deal with.

<b>Yes, you should be asking for genetic testing.</b>

Please read my blog page for more information about my kids, their sweat tests and health issues.

 

[PedsNP2007]

Has she been tested for her immune function?

 

[kate620]

My daughter had I think 6 sweat tests. Half were positive and half were negative! The CF center said she would not have a negative if she had CF. She also had pnemonia as a baby and RSV when she was 2. Her gene test only showed 1 gene so they thought she was just a carrier. Another test they could do is on her poop to see if she absorbs her fats. My daughter does so they told me that was rare for someone with CF to do that. But she was really constipated like yours so she is on Miralax. When she was a baby she even tore her butt from trying to poop. It was sad. I knew something was wrong. But boy did I pray it wasnt CF. She had too many pieces of the puzzle tho. I took her to another CF clinic an hr away and the first visit they did a throat swab and it was positive for pseudomonas aeroginosa( a bacteria that grows only in CF lungs) so she was finally diagnosed. It took 1 1/2 yrs! So therefor, I definately recommend a 2nd opinion even if a CF center doesnt think so. Make sure they cover ALL bases not just a sweat test.