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Sweat test - ionotophoresis - limiting values
- Question
- Dear ladies and gentlemen,
our son (10) has had now already the third sweat test at a CF- center. The results varied:
76 mmol/l NaCl, 72 mmol/l NaCl and 59 mmol/l NaCl.
I would be interested in the limiting values and the reasons for the variation.
We are still waiting on the results of the human genetics. As our son is otherwise free of symptoms, and is pancreas sufficient, we are patient.
Thanks in advance! - Answer
- Hello,
You ask for the reasons of the variability of the sweat test results of your son. In general it can be said, that the electrolyte values of the sweat of a human being are under normal circumstances very stable and do not show great variations. The results of 72 resp. 76 mmol/l for NaCl has to be judged as a normal variation range of that laboratory. The value of 59 mmol/l does vary too much here. One can only explain that with a measuring error or a dilution error of the laboratory. After very strong losses of sweat one can see in single cases a slight decrease of the sweat electrolyte values. This could probably be an explanation of the difference.
In addition, you mention, that you were interested in the limiting values. It has to be stated, that for interpreting a sweat test, the sweat chloride is the only analyte, on which a diagnosis of CF should be based. In your question, however, you mention only NaCl values, means the sodium chloride values. So, as we do not know which method has been used here, we can not comment on the mentioned values. A correct sweat test is based on a so-called pilocarpine ionotophoresis stimulation of the sweat. After collection, the chloride concentration is measured. For children over the age of 6 months, there are the following limiting values for the sole sweat chloride:
under 40 mmol/l, CF unlikely, 40-60 mmol/l intermediate, which make furhter investigations necessary, over 60 mmo/l indicative of CF.
We hope, that with the molecular genetic investigation the unpleasant waiting situation will be clarified soon.
Yours sincerely,
Dr. H.-G. Posselt - 07.07.2009
