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A sweat test measures the amount of salt chemicals (sodium and chloride) in sweat. It is done to help diagnose cystic fibrosis. Normally, sweat on the skin surface contains very little sodium and chloride. People with cystic fibrosis have 2 to 5 times the normal amount of sodium and chloride in their sweat.
During the sweat test, medicine that causes a person to sweat is applied to the skin (usually on the arm or thigh). The sweat is then collected on a paper or a gauze pad, and the amount of salt chemicals in the paper or gauze is measured in a lab. Generally, chloride (sweat chloride) is measured.
This test may be done as soon as your baby is 10 days old, but it is often done when a baby is 2 to 4 weeks of age. Your child may need more than one sweat test to confirm if he or she has cystic fibrosis.
The sweat test is done to help diagnose cystic fibrosis. It also may be used to test people with a family history of cystic fibrosis and for anyone with symptoms of cystic fibrosis.
No special preparation is needed before having this test. Your child may eat, drink, and exercise normally before the test. If your child takes any medicines, give them on the usual schedule.
You may help with the test and stay with your child during the test. If you can't stay, you may want to ask a family member or friend to stay with your child. Bring your child's favorite book or toy to help pass the time while the test is done. See if your child might be able to watch a movie during the test.
The sweat test is usually done on a baby's arm or thigh. On an older child or adult, the test is usually done on the inside of the forearm. Sweat is usually collected and analyzed from two different sites.
The sweat test usually takes 45 minutes to 1 hour.
This test does not cause pain. Some children feel a light tingling or tickling when the electric current is applied to the skin. If the gauze pads are not properly placed, the electric current may produce a burning sensation.
There is very little risk of complications from this test. But the test should always be done on an arm or leg (not the chest) to prevent the possibility of electric shock.
The electric current may cause skin redness and excess sweating for a short time after the test is done. In rare cases, the current may make the skin look slightly sunburned.
Results are usually available in 1 or 2 days.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
Less than 40 millimoles per liter (mmol/L)
60 mmol/L or more
Less than 30 mmol/L
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.
Farrell PM, et al. (2008). Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic Fibrosis Foundation consensus report. Journal of Pediatrics, 153(2): S4–S14.
Current as of:
September 23, 2020
Author: Healthwise StaffMedical Review: John Pope MD - PediatricsKathleen Romito MD - Family MedicineR. Steven Tharratt MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology
Current as of: September 23, 2020
Author: Healthwise Staff
Medical Review:John Pope MD - Pediatrics & Kathleen Romito MD - Family Medicine & R. Steven Tharratt MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology
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