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Sweat Test

Results

A sweat test measures the amount of salt chemicals (sodium and chloride) in sweat. Generally, chloride (sweat chloride) is measured.

Results are usually available in 1 or 2 days. Normal results vary from lab to lab.

Sweat chloride in people age 6 months and older 1
Normal:

Less than 40 millimoles per liter (mmol/L)

Borderline:

40–59 mmol/L

Abnormal:

60 mmol/L or more

Sweat chloride in babies younger than 6 months 1
Normal:

Less than 30 mmol/L

Borderline:

30–59 mmol/L

Abnormal:

60 mmol/L or more

Many conditions can change sodium and chloride levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.

The test results do not show how severe the cystic fibrosis is. The test only shows if a person could have the disease.

Abnormal (high) values

High values:

  • Usually mean that a person has cystic fibrosis. Some people with cystic fibrosis have borderline or even normal sweat chloride levels.
  • May be caused by other conditions. But the sweat test is not used to diagnose these conditions, which include:

What Affects the Test

Reasons your child may not be able to have the test or why the results may not be helpful include:

  • A baby's age. Babies younger than 2 weeks may not produce enough sweat to give reliable test results and may have lower sweat chloride levels than older babies and children. A minimum amount of sweat is needed for accurate test results regardless of the child's age.
  • A skin rash or sore on the area of the skin where the gauze pads are attached.
  • Acute or severe illness.
  • Dehydration or heavy sweating.
  • Decreased sweating.
  • Normal fluctuations in sodium and chloride during puberty.
  • A decrease in the hormone aldosterone.
  • Steroid medicines, such as fludrocortisone.

WebMD Medical Reference from Healthwise

Last Updated: July 18, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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