Cystic Fibrosis (CF) Chloride Sweat Test

What It Is

A chloride sweat test helps diagnose cystic fibrosis (CF), an inherited disorder that makes kids sick by disrupting the normal function of epithelial cells. These cells make up the sweat glands in the skin and also line passageways inside the lungs, liver, pancreas, and digestive and reproductive systems. Kids who have CF are at risk for repeated lung infections.

The sweat test measures the amount of chloride in sweat. Kids with cystic fibrosis can have two to five times the normal amount of chloride in their sweat. In a sweat test, the skin is stimulated to produce enough sweat to be absorbed into a special collector and then analyzed.

Doctors may test an infant suspected of having cystic fibrosis as early as 48 hours after birth, though any test done during a baby's first month might need to be repeated because newborns may not produce enough sweat to ensure reliable results.

Why It's Done

Doctors will order a chloride sweat test for kids with positive newborn screen for cystic fibrosis, a family history of cystic fibrosis, or symptoms of the disorder. Symptoms and signs include failure to grow, repeated lung infections, and digestive problems.

Preparation

No special preparation is necessary for this test. Before having this test, your child may eat, drink, and exercise as usual, and continue to take any current medicines. Creams and lotions should not be applied to the skin 24 hours before the procedure. A sweat test usually takes about an hour, so you may want to bring books or toys to help your child pass the time.