Cystic fibrosis sweat test
What is this test?
This test measures the concentration of chloride in sweat from the body. This test is used to diagnose cystic fibrosis.
What are other names for this test?
- Chloride measurement, sweat
- Sweat chloride
- Sweat chloride level
What are related tests?
Why do I need this test?
Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. The following is a possible reason why this test may be done:
When and how often should I have this test?
When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.
Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.
The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.
How should I get ready for the test?
Do not apply creams or lotions to your child’s skin for 24 hours before the sweat test.
How is the test done?
A sweat test generally takes about 45 minutes to complete. Your child’s skin will be cleaned and a special chemical that causes sweating will be applied to a small patch of skin on your child’s arm or leg. Adhesive patches called electrodes will be placed on the arm or leg. For about five minutes, the electrodes transmit a very weak electrical current that causes sweating.
The pads are then removed and the area washed. A dry pad will then be placed on the same area where the electrodes were. It is covered in a special plastic which traps any sweat produced. After 30 to 40 minutes, the pad will be removed and the sweat in it will be collected.
How will the test feel?
During a sweat test, your child may feel a warm or tickling sensation. This test is usually not painful or uncomfortable.
What should I do after the test?
There are no special instructions to follow after this test.
What are the risks?
Sweat: A sweat test is generally considered safe. Talk to your child’s healthcare worker if you have any questions or concerns about this test.
What are normal results for this test?
Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following is considered to be a normal result for this test:
- Adults and Children: <40 mmol/L 
What follow up should I do after this test?
Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.
Where can I get more information?
- Leigh MW: Diagnosis of CF despite normal or borderline sweat chloride. Paediatr Respir Rev 2004; 5(Suppl A):S357-S359.
- Baumer JH: Evidence based guidelines for the performance of the sweat test for the investigation of cystic fibrosis in the UK. Arch Dis Child 2003; 88:1126-1127.
- Wang L & Freedman SD: Laboratory tests for the diagnosis of cystic fibrosis. Am J Clin Pathol 2002; 117 (Suppl 1):S109-S115.
- Lebecque P, Leal T, De Boeck C, et al: Mutations of the cystic fibrosis gene and intermediate sweat chloride levels in children. Am J Respir Crit Care Med 2002; 165:757-761.