CF – initial diagnosis during adulthood – sweat test

Question

Hello Expert Team,

how reliable are sweat tests for a diagnosis during adulthood?

Should it be taken several times if the first result was in the gray area (with this particular machine: 88 – positive; result – 68).

Thank you very much in advance for your help.

Regards,
simmy

Answer

Hello,

According to the current level of knowledge, regardless of the patient’s age, the sweat test is gold standard for the diagnosis of CF – provided that it is carried out correctly. Therefore, we always recommend taking a sweat test at a CF center.

In the diagnosis, the sweat test always has to be linked to the medical condition and the clinical picture.

If the diagnosis remains questionable after a controlled sweat test, it is recommended to do a genetic analysis.

In case of doubt, if the genetic finding is unclear, a nasal potential difference (PD) measurement or an intestinal current measurement (ICM) can be performed supportively.

The sweat test should be carried out as a Pilocarpine Iontophoresis and not as a conductivity measurement. The sweat test consists of 5-10 min of skin stimulation and a 30-60 min collection period afterwards. Here, sodium (flame photometry) and chloride (titration) are measured.

Values for chloride and sodium (minimum amount of 40 ul required):
- pathological: >60 mmol/l (>70 mmol/l in adults, respectively)
- to be followed up: >30 mmol/l

Back to your question:
- Please check if your sweat test was taken in compliance with the existing rules
- If the result is in the gray area, another test should be done.
- For affected persons, we recommend seeing a CF-competent doctor to have the test results clarified in a personal consultation.

I hope this answer helps.

Kind regards,
Dr. C. Smaczny

15.01.2009