Acute/abating pneumonia as counterindication for a sweat test?

Question

The title already indicates my question.

For seven months, our 19-month-old daughter has repeatedly been battling a cough that could not be healed completely (Spasmo-Mucosolvan®, Mucosolvan®, salbutamol and Salbubronch®). She has not been coughing much, but actually with only few interruptions since turning one.

Now she has been diagnosed with acute pneumonia a few days ago (which is taking up about 1/4 to 1/3 of the right lung). The pneumonia involved a fever of up to 40.5°C over a period of four days. On the fifth day (second day of antibiotics treatment), the fever went down even without antipyretic drugs (ibuprofen, paracetamol).

She has eaten very little since, though now her appetite is coming back. On the other hand, she has been drinking a bit more than usual.

We have scheduled a sweat test for tomorrow (third day without fever) to check for CF.

Is an acute, feverish cold with accompanying diarrhoea a counter-indication for a sweat test? Should we postpone the test for a week or two?

Many thanks.

Answer

Hello,

Your 19-moth-old-daughter has been having increasing cough for about 7 months and has actually been coughing since her first birthday. She has been diagnosed with pneumonia. At the beginning, she ran a high fever that disappeared after the third day of antibiotics therapy. Currently there is a sweat test scheduled on suspicion of CF. Since this test would be carried out already on the third day after the fever went away, you are asking whether a recent infection like this (pneumonia) constitutes a counter-indication for a sweat test. You mention that your daughter temporarily had diarrhoea during the infection and that she ate little but drank more than usual. You would like to clarify with your question whether the sweat test results could be affected by the infection that your daughter just recently had.

In the context of a feverish infection accompanied by diarrhoea, there can be alterations in the sweat test if there is also severe dehydration involved (exsiccosis). This usually leads to falsely increased values as long as the salt balance has not derailed completely, that is, if there has been a “thickening” of the blood with elevated salt levels. In very rare cases, with a high loss of blood salt, it can also lead to falsely lower sweat test results.

According to your description, neither the former (a form of derailment of the salt balance) nor the latter (high loss of blood salt) is the case. One can therefore reckon that the test result will be reliable. The treating doctors probably want to get clarity as quickly as possible given that the CF diagnosis is still unresolved. Of course, this is also in your own interest, since doing the test quickly will shorten the time of uncertainty and thus the time of potentially unnecessary worries.

Good luck!

Kind regards
Dr. H.-G. Posselt

02.08.2012