Falsification of CF sweat test result?

Question

If our daughter did a sweat test in the hospital while having an infection (pneumonia) and taking cortisone and inhaling salbutamol, will the test result (which was negative in our case) be falsified?

We heard that an infection and various drugs can skew the sweat test result. Our pediatrician says this is true, but then the result would be shifted towards the positive and not at all be negative. A second opinion said yes, but it could generally be falsified in both directions (positive as well as negative)?!? Which one is right???

Answer

Hello,

you are asking whether the result of a sweat test can be falsified by cortisone or salbutamol therapy.

Administration of salbutamol does not have a noteworthy effect on the result of a sweat test. Cortisone administration can affect the result minimally. It can reduce the values by about 10-15%. Thus a result from the “slightly increased” range could be pushed to the threshold range, or from the “threshold range” to the normal range. This means that there is only the possibility of a slight variation, which is only to be expected if a larger amount of cortisone (2mg/kg body weight) was administered orally or intravenously.

Concerning an infection, it has to be said that a very severe infection with long-lasting fever, strong perspiration and obvious signs of a dehydration can change the result of a sweat test. In case we have a loss of salt, the value could be decreased. In case there is no loss of salt, the value can be increased.

To rule out any uncertainties, I would suggest repeating the sweat test for your reassurance.

Kind regards
Dr. H.-G. Posselt

13.09.2010