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Abnormal sweat test

My 6 year old has had complications from birth. At 6 weeks old he was hospitalized for an extended length in time for R.S.V. and has issues since then. He has had bronchitis a few times, croup, had two adenoid removal surgeries, a tonsillectomy, been diagnosed with chronic sinusitis, and is generally always sick. He coughs up lots of dark green and yellow phlegm, and has coughed up blood several times (which has been said to be due to the sinusitis). He also just has his nasal passages opened because the infection was to thick to drain on it's own. Meds don't clear it up.We recently started seeing a new doctor because his last doctor kept saying it was allergies and asthma and all of the medication he put him on wasn't working. The new doctor wanted to start over and rule out everything to try to get to the bottom of his illnesses and sent him for a sweat test. I received a phone call last week that his test results were abnormal (his sodium chloride level is a 53) and we are now being referred to a children's hospital for further testing. I was just wondering what the outcome of the second tests may be (are they usually similar to the first results?) and how likely it is that he would be diagnosed with cystic fibrosis or atypical cystic fibrosis. He is mildly salty when I kiss him and his bowel movements are sticky and tar like at times, and also strange colors (like bright blue, green or yellow). Thank you
Dear Parent

Thank you for your question regarding your child.
The diagnosis of CF is usually made on the basis of several tests. Sometimes the diagnosis is clear cut when a person has two CF causing mutations and a clearly positive sweat test. However as there is a complete spectrum of disease people at the milder end of the spectrum may be more difficult to diagnose conclusively.
In these cases it is a combination of the sweat test, genetics, faecal elastase level,NPD(nasal potential differences), family history and symptoms, which may help to decide the diagnosis.
Certain mutations in CF are known to be associated with borderline or normal sweat tests eg R117H, D115214, G551S. At times those at the milder end of the spectrum with a borderline sweat test result may become more positive over time. Those with a borderline sweat test do need further investigation and ongoing follow up.

If your doctor is planning to carry out further testing this is likely to involve repeating the sweat test, sending blood for DNA analysis for the most common CF mutations, sometimes nasal potential differences are checked and faecal elastase samples can also be sent.
If the sweat test remains borderline and the genetics do not reveal two mutations the diagnosis may remain inconclusive.
Your doctor may decide that the diagnosis is in keeping with CFTR related disorder / CF related metabolic disorder.
Certainly your child does seem to have had a lot of symptoms and with an inconclusive sweat test it is appropriate for further investigations to be carried out. Please discuss this with your local clinician.
I hope you get definitive diagnosis for your child.

Dr Laura Jenkins
CF Associate Specialist Doctor(Paediatrics)

1.Guidelines for the diagnosis of Cystic Fibrosis in newborns through to older adults : CFF consensus report
J. Pediatr 2008, August 153(2) S4-S14 (can be accessed on line)

The answer is edited by: Laura Jenkins