cystic fibrosis-sweat test

Question

I have a 9 year old daughter with diarrhea since birth, the genetic test was negative for 29 mutations, but the symptoms and the sweat test was 68 NaCl, 58 and the lowest value 48 NaCl. How many registered patients have a positive genetic test? My daughter
also has respiratory tract infection with Staphylococcus aureus for 3 years, adenoidectomy and viscous secretions of the noose and stool. What should I do?

Answer

Dear questioner, you report 3 sweat test values. In here, it is of high importance that those values are chloride values in the sweat (not NaCl) measured by pilocarpine ionotophoresis, and that those tests have been performed in a experienced center. Chloride values under 40 mmol/l are negative, between 40-60 mmol/l are in the borderline area, over 60 mmol/l are regarded positive. So it seems that 2 values were in the borderline area, and one was pathologic.
So in case the sweat test results are not conclusive (assumed the test has been done correctly at an experienced center, probably another test should be performed), further diagnostics measures have to be performed, such as pancreatic function tests (e.g. measurement of the pancreatic elastase in the stool or fat excretion in the stool), clinical assessment, x-ray, respiratory tract culture for CF-associated pathogens or genetic testing for CFTR mutations. The test for 29 mutations, that was done in your daughter, was negative, but there is a possibility , that there is a mutation which can not be detected by this 29-mutations panel, so an extended genetic analysis could be an option. However, even with an extended investigation (like investigation a larger mutation panel or even sequencing the whole gene) the diagnosis in rare cases not be made a 100% sure, as there might be unkonwn mutations for example.
Even if the diagnosis cannot be made 100% sure, but there is the clinical suspicion of CF (fatty stools, failure to thrive, pulmonary symptoms as cough and infections, chronic rhinosinusitis), it is most important to monitor the clinical course of the child and if necessary to initiate a therapy.
We suggest a reassessment of the diagnosis.
Sincerely, Prof.dr.Liviu Pop and Dr. Daniela d'Alquen

07.06.2011