What is being tested?
Sodium and chloride are part of your body’s electrolyte balance. They help regulate the fluid balance in your blood and tissues. Normally, chloride travels in and out of the body’s cells, helping to maintain electrical neutrality and water balance. Chloride’s level usually mirrors that of sodium.

When a patient has cystic fibrosis (CF), they have inherited a mutated (abnormal) pair of genes on chromosome number 7. These genes normally produce a protein (cystic fibrosis transmembrane conductance regulator (CFTR)) that serves as a channel, letting chloride out of cells and into the surrounding fluid. When a mutation is present, the CFTR protein may not work properly or be totally absent. Since CFTR levels are usually highest in the cells lining the internal surfaces of the pancreas, sweat glands, salivary glands, intestine, and reproductive organs, these are the areas most affected by CF.

The cells absorb more water than normal, making the mucous and secretions thick and sticky and the sweat about five times saltier than normal. This elevation in salt in the sweat can be measured, as a sweat chloride test.

How is the sample collected for testing?
A sweat sample is collected using a special sweat stimulation procedure. A tiny amount of a clear, sweat-stimulating liquid is applied to a small patch of skin on the arm or leg. An electrode is then placed over the site and a weak electrical current stimulates the area. This is a painless procedure that may create a tingling or warm sensation. After several minutes, the area is cleaned and sweat is collected for about thirty minutes, either into a plastic coil of tubing or onto a piece of gauze or filter paper. The sweat obtained is then sent to the laboratory for analysis.