Sweat electrolytes

Alternative names
Sweat test; Sweat chloride; Iontophoretic sweat test

Definition
This is a test that measures the level of chloride in sweat.

How the test is performed

A low-level electric current is applied to the test area. The positive electrode is covered by gauze and saturated with pilocarpine (a drug that stimulates sweating). The negative electrode is covered with gauze and saturated with bicarbonate solution.

A current is applied for 5 to 12 minutes, and a paper disk is then placed over the test site and covered with paraffin to obtain an airtight seal. After 1 hour, the disk is transferred to a weighing jar, then put in water to dissolve the salts. This solution is then analyzed for chloride.

How to prepare for the test
No special preparation is necessary.

How the test will feel
The test does not cause any discomfort.

Why the test is performed
Children with cystic fibrosis have increased sodium and chloride concentrations in their sweat. The test may be performed on infants to determine if early therapy is needed.

Normal Values

Normal Values are as follows:

     
  • Sodium:       o Normal: less than 70 mEq/L       o Abnormal: greater than 90 mEq/L       o Equivocal: 70 to 90 mEq/L  
  • Chloride:       o Normal: less than 50 mEq/L       o Abnormal: greater than 60 mEq/L       o Equivocal: 50 to 60 mEq/L

Note: mEq/L = milliequivalent per liter

What abnormal results mean
An abnormal test may indicate the presence of cystic fibrosis.

Johns Hopkins patient information

Last revised: December 3, 2012
by Gevorg A. Poghosian, Ph.D.

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