A sweat test measures the amount of chloride and sodium (salt) in the patient’s sweat. This test is the best way of checking for a health problem called cystic fibrosis (CF). Most babies who get a sweat test do not have CF, but it's important to "rule it out."
Before the Sweat Test
Do not use any lotions or creams on your baby's arms or legs on the day of the test (including moisturizing soaps). Bring an extra blanket or sweater and hat to keep the baby warm during the test.
What to Expect
The sweat test takes about one hour from start to finish. A special machine causes a small part of the baby's arm or leg to sweat. The skin may feel warm and tingly for 5 minutes while the machine is on. Your baby may cry during this part of the test, but it is not painful. The sweat is collected on a gauze pad or disc. After 30 minutes time, the gauze or disc is removed and the sweat is tested in the lab.
What Do the Results Mean?
Results should be available by the morning after the test. There are four possible results:
Negative result: This means that a normal amount of salt was found in the sweat. It is very rare for a person to have CF if the sweat test result is negative. Your baby should get regular baby care.
Positive result: A positive sweat test means that your baby probably has CF. The baby should have a second sweat test and a check-up with a doctor who specializes in treating people with CF.
Borderline result: Sometimes the sweat test result will be in between positive and negative. You will be asked to bring the baby back for another sweat test, and perhaps an exam and blood test.
"QNS": This means Quantity Not Sufficient (there was not enough sweat on the gauze or disc). You will be asked to bring the baby back another day to try again.