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Oral intake & Sweat Test result

Dear Sir / Ma'am,

I have had the following email sent to the email part of our Helpline and I wouldered if someone knows the answer: -

This may be a strange question-

Is there any information as to whether certain medications, supplements, or a diet with too much salt can cause a false positive on a CF sweat test?

I appreciate your taking the time,

Thank you,


Kind regards,
[The question was answered by a German expert]

Dear questioner,

I found in the literature a list of conditions which can lead to an increased chloride concentration in the sweat, therefore a false positive sweat test (source: von Mutius, Gappa, Eber, Frey: “Pediatric pneumolgy, 3rd edition 2014, Spinger Verlag, Germany). Here comes the list:
Adrenal insufficiency
Anorexia nervosa
Atopic dermatitis
Autonomic dysfunction
Coeliac disease
Ectodermal dysplasia
Familial cholestasis (Byler’s disease)
G6PD deficiency
Glycogen storage disease type 1
Klinefelter's syndrome
Long-term infusion of PEG1
Mucopolysaccharidosis type 1
Nephrogenic diabetes insipidus
Psychosocial problems
To address concretely the terms medication, supplements or diet:

1) Medications/supplements: by searching the literature, I found a statement, that cortisone intake of round about 2mg/kg body weight and day or in higher concentrations may lower the chloride concentration in the sweat about 10-15%, that means the sweat test could be false negative (not positive as asked in your question) under a high dose cortisone therapy.

On the other hand, you see that in the list, an adrenal insufficiency could lead to a false positive sweat test, as in that case, there is a lack of the hormones aldosterone and cortisone that are produced by the body itself.

Also medications that influence the thyroid gland (blockers of the thyroid gland) could result in false positive sweat test, as the condition “Hypothyreoidism” is listed above.
Apart from cortisone, I could only find a report about the anticonvulsant Topiramate, that has been shown in 2012 to cause elevated sweat chloride levels in patients not suffering from CF (Guglani L et al.: “Elevated sweat chloride concentration in children without cystic fibrosis who are receiving topiramate therapy.” Pediatr Pulmonol. 2012 May;47(5):429-33). Let me cite the last sentence of the abstract: “This is the first report of a medication affecting sweat chloride values and shows that topiramate therapy can cause elevated sweat chloride concentrations in the absence of clinical manifestations of CF.”
Therefore I have to date no other information on drugs that could influence the sweat test results.

2) Diet: As you can see from the list, malnutrition like e.g. found in case of anorexia nervosa, can lead to false positive sweat test results. If there is insufficient fluid intake or excessive loss of fluid e.g. via fever, diarrhea or vomiting, a dehydration can also be the reason for increased sweat chloride concentrations.

If you have an undiscovered caeliac disease and eat a normal (not gluten free) diet, increased sweat chloride levels can result. Please see all other metabolic disorders that could cause false positive sweat test results in the list.

I could not find a statement in the literature, that the intake of too much salt could be the reason for an increased chloride concentration in the sweat. Increased intake of salt is normally answered by the body with increased thurst, so that the drunken water compensates the increased salt concentration in the blood; furthermore, the kidneys will excrete the remaining salt. But be aware that on the other hand, if your sweat has an increased salt concentration due to an underlying CF, and you sweat because of physical activity, you will have an increased salt loss.

I hope to have answered your question and stay with best regards,

Dr. Daniela d’Alquen (coordinator of the Central English Archive of ECORN.CF)