This article outlines the purpose of sweat tests and provides tips on how to prepare, what to expect, and how to understand the results.
Purpose of Test
The purpose of a sweat test is to measure the amount of chloride in a person’s sweat, which can help diagnose cystic fibrosis, or CF. Chloride, a type of electrolyte, is normally present in bodily fluids like sweat—but too much or too little of it can indicate a potential health concern.
In people with CF, chloride levels can be much higher than average. This results in an accumulation of chloride in the lungs, bile ducts, pancreatic ducts, small intestines, and the surface of the skin.
A healthcare provider will order a sweat test when certain CF symptoms are present, such as breathing problems, lung infections, poor growth, and weight loss. Sometimes, genetic testing is recommended to confirm the sweat test results because there are genetic mutations associated with the disease.
Though CF is usually diagnosed in infancy, sweat tests are for people of all ages in case CF goes undetected into adulthood.
Risks and Contraindications
First introduced in 1959, experts consider the sweat test to be extremely reliable and accurate for diagnosing CF.
There aren’t any risks associated with this test, and it’s generally not painful or uncomfortable. The sweat test is also appropriate for any age group. It’s recommended that infants are at least a few days old so they can produce enough sweat to get accurate results.
Before the Test
According to the Cystic Fibrosis Foundation (CFF), a sweat test should take place within two weeks of when a healthcare provider recommends it. Though there’s not much physical preparation needed on the patient’s part, there is some information that’s helpful to know ahead of the test.
Timing
From start to finish, expect to spend more than an hour at the facility. The sweat-collecting portion of the test will take roughly 30 minutes, but there is some setup required. It may also take a bit of time to fill out routine paperwork and wait to be called back to the exam room.
Location
A sweat test typically takes place at a hospital or outpatient health center. CFF recommends CFF-accredited care centers to ensure the accuracy of the results. There are more than 130 of these locations across the country at teaching and community hospitals.
The room setup will look typical of a regular hospital or doctor’s office room, with a place for the patient to sit or lie down and a small electrode device nearby that helps the technician perform the test.
What to Wear
You can wear normal clothes to the sweat test, but your healthcare provider may recommend bringing warm clothing or a blanket to help prompt sweating. Note that the technician will need access to the patient’s arms or legs to place the electrodes on for the actual test, so they may provide a hospital gown.
Food and Drink
Patients can eat, drink, and take medications regularly ahead of the sweat test. It’s a good idea to be well hydrated when arriving for the test, so the body’s sweating function is working properly.
The only pretest guidance is to not apply creams or lotions to the skin 24 hours before the test because it could interfere with the results.
Cost and Health Insurance
Sweat testing is covered under many insurance plans, though the cost will vary by plan and location.
For people who do not have access to insurance, the University of Michigan Health System notes that the cost of a sweat test at their facility is $617.
What to Bring
Check with your healthcare provider or testing location to see if there are any specific items—such as paperwork, health insurance information, or an identification card—that they need from you at the appointment.
You might consider bringing toys or books to help entertain your child or baby if they are the ones undergoing the sweat test.
During the Test
On the day of your test, you will first register at the front desk of the facility. This usually includes confirming your insurance information, if applicable, and filling out forms related to the test.
You’ll then be brought back to the exam room where the test will take place. The sweat test is usually performed by a special technician, though an attending healthcare provider may also be present.
Pretest
When in the exam room, you can typically remain in the normal clothing you came in as long as the technician has access to your arm or leg. You may have been advised to bring a blanket and/or warmer clothing from home to help the sweating process.
No intravenous (IV) or oral medications are involved here, so the test will start when the technician is set up and ready to begin.
Throughout the Test
The patient will first be asked to expose their forearm—or sometimes their thigh for babies—so the skin around the testing area can be cleaned and prepped for the test. No needles are involved here.
During the first part of the test, a chemical called pilocarpine is applied to a small part of the arm or leg. Then, a tool called an electrode is applied to the area to add electrical stimulation. Together, this prompts the sweat glands in the skin to produce sweat. It’s possible to feel a slight tingling or tickling during this time, but many people don’t feel any discomfort at all.
After 10 minutes or so, the electrical stimulation is stopped and the electrode is removed. The technician will wipe the area of the skin and add a piece of filter paper, gauze, or plastic coil. This step is the collection of the actual sweat and can take several minutes.
From there, the paper is removed and the sweat sample is sent to a hospital laboratory to measure how much chloride is in the sweat. This will happen later the same day or the next business day.
Post-Test
After the test is done, there are no special steps or recovery precautions to take. Though it’s possible that the tested skin may remain a bit red for an hour or two after the procedure, there shouldn’t be any pain or restrictions involved.
After the Test
Following a sweat test, patients are free to resume their normal activities—eating, drinking, and going about their day as soon as the test ends.
Interpreting Results
Most sweat test results from the laboratory are returned to your healthcare provider within a business day or two. Some facilities may be able to provide results later that same day, so make sure you ask staff when to expect results.
The results will determine whether or not the person has CF based on the amount of chloride in the sweat sample. The diagnostic ranges for children and adults are usually as follows:
Negative result: Chloride level is less than 30 mmol/LPositive result: Chloride level is greater than 60 mmol/LBorderline result: Chloride level is between 30 and 59 mmol/L
Your healthcare provider will be able to talk through these results with you and let you know what the exact diagnosis is.
Follow-Up
In some cases, the sweat test may need to be repeated. This could happen if:
The amount of sweat collected isn’t enough to give a conclusive or accurate result (more common with infants). The sweat sample was contaminated. The result came back within the “borderline” range.
Your healthcare provider may also order additional follow-up tests related to a CF diagnosis. For example, a chest X-ray or upper GI series could check for lung and digestive issues that are common with CF.
Summary
Sweat tests measure the amount of chloride (an electrolyte) in your sweat. They help diagnose cystic fibrosis (or CF), a genetic disorder that primarily affects the lungs and causes higher levels of chloride on the skin. A healthcare provider will recommend this test if CF symptoms are present or if there is a family history of the disease.
This test usually takes about an hour, is not painful, and does not have any risks associated with it. It involves a technician collecting sweat from a small area of the arm or leg by using a special solution and an electric current tool. Sweat tests are highly accurate and are for people of any age, though CF is most often detected in infancy.
A Word From Verywell
If you’ve found out that you or your child requires a sweat test, you’re not alone. Cystic fibrosis is a fairly common genetic condition in the United States. You can find more information, resources, and support from the Cystic Fibrosis Foundation, which offers programs and services to people with the disease.
