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Old 04-15-2009, 07:15 AM   #1
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positive sweat test x 2 but no cf gene why

My son is 12 years old and was dig, with cf at 7 for failure to trive low weight gain and a bone age 2-3 years behind his actual age. Since then he has a failed peg fitted, followed by an N G. now he has a Mic-Key fitted. He never had chest infections but does grow unusual bugs in the throat area. Recently he had DNA testing to find out what CF gene he has but no Gene was found. I am waiting for the new appointment for another sweat test. The first two were done at 6.5 years and both positive. 68 and 73. But does he have CF? His pft's are around 112 average.

 
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Old 04-21-2009, 12:47 PM   #2
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Re: positive sweat test x 2 but no cf gene why

How many mutations did they test for? Did they do a basic panel or ambry amplified? Ambry amplified tests for over 1400 different cf mutations, deletions, etc. With sweat test #s that high, I would hope that a doctor would push for answers. Don't think I've ever heard of a false positive with sweat tests, just a false negative.

 
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Old 04-22-2009, 03:46 AM   #3
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Re: positive sweat test x 2 but no cf gene why

I believe it was around 400 or so. Our new appointment is for the 24 June 09 for a repeat sweat test. Since he came off his creon he has lost weight 2.5kg so although his stool sample showed that the pancreas is producing enzymes it does not explain why he is loosing weight even with night feeds. I think he needs to go back on the creon but will wait till the results are back.

Siobhan

 
Old 07-14-2010, 06:26 PM   #4
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Re: positive sweat test x 2 but no cf gene why

Our son has had similar test results Positive Sweat test but gene test showed no mutations out of 1400 tested - did you find anything

 
Old 07-15-2010, 01:34 AM   #5
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Re: positive sweat test x 2 but no cf gene why

Hi,
after treating my son for 7 years for CF it turns out he has not got Cf, what they said about not finding the cf gene was that unless he had one of the common ones it is possible that he had a rare one and so they were happy to treat him as a cf patient. Only after a normal NPD test in september did they reverse the diagnosis. Dont let them label your child unless they are 100% certain, my child and my family went through hell with treatments, medication, surgery for feeding tubes etc

 
Old 07-15-2010, 07:29 AM   #6
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Re: positive sweat test x 2 but no cf gene why

Thank you so much for the information - I am sorry you and your family went through the medical hell but I am glad to hear that he does not have CF

 
Old 07-15-2010, 07:31 AM   #7
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Re: positive sweat test x 2 but no cf gene why

I am however curious what an NPD test is and what does it tell you?

 
Old 07-15-2010, 09:10 AM   #8
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Re: positive sweat test x 2 but no cf gene why

So are we, However although they have removed the title of CF they have still left a question over what if anything has he got.
Anyway best wishes for you and your family.

Siobhan

 
Old 07-15-2010, 09:23 AM   #9
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Re: positive sweat test x 2 but no cf gene why

What is a NPD Test and what does it do?

 
Old 07-15-2010, 11:45 AM   #10
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Re: positive sweat test x 2 but no cf gene why

Quote:
Originally Posted by XiMaker View Post
What is a NPD Test and what does it do?
an NPD or Nasal potential dirrerence is used to test for the amount of sodium carried between the nasal passage area and the cells present there. My son show'd no signs of sodium or only normal amounts.
In a patient with CF it would be abnormal and this test is only carried out in London, surprise surprise Ireland is still dragging itself out of the dark ages.

Siobhan

 
Old 11-17-2010, 01:59 AM   #11
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Re: positive sweat test x 2 but no cf gene why

Hi!

I to have a daughter with elevated sweat chloride results and no known genes. She has classic CF signs and was diagnosed years ago despite her very shy genes.

If your son has symptoms and the medicines and therapy help him, I would certainly keep doing them.

They do not know everything about CF. In fact, it is changing at lighting speed....

I would not necessarily rule CF out based on your sons test results...

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1320177/

Nasal Potential Difference
The impaired ion transport of CF respiratory epithelia can be studied in vivo by measuring the potential difference (NPD) in nasal mucosa.47 This is a significantly more complex test of CFTR function than measurement of sweat electrolytes. The protocol for NPD is well described and standardised but performed in only specialised (mostly adult) centres.48 Patients with CF have reduced chloride transport with sodium hyperabsorption, measured as a more negative basal potential difference. Perfusion with the sodium channel blocker amiloride results in a greater drop in NPD in CF patients, while perfusion with chloride-free solution and isoproterenol to stimulate CFTR function has no effect. NPD may complement sweat testing and CFTR mutation analysis.

However, it may also produce indeterminate results, particularly in “borderline” cases.49,50 NPD measurement is technically difficult and requires extensive experience for proper conduct and interpretation.51 Only one centre has reported use of NPD in infants.52 The presence of nasal inflammation, as in allergic rhinitis or viral infection, can alter ion transport and result in false negative results.48

For patients in whom both the sweat test and mutation analysis are inconclusive, an abnormal nasal PD measurement can be used as evidence of CFTR dysfunction.38

Last edited by moderator2; 11-17-2010 at 04:59 AM.

 
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