Sweat Test
How It Feels
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.
Risks
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
A sweat test measures the amount of salt chemicals (sodium and chloride) in sweat. Generally, chloride (sweat chloride) is measured.
Results are usually available in 1 or 2 days. Normal results vary from lab to lab.
| Normal: | Less than 40 millimoles per liter (mmol/L) |
|---|---|
| Borderline: | 40-59 mmol/L |
| Abnormal: | 60 mmol/L or more |
| Normal: | Less than 30 mmol/L |
|---|---|
| Borderline: | 30-59 mmol/L |
| Abnormal: | 60 mmol/L or more |
Many conditions can change sodium and chloride levels. Your health professional will discuss any significant abnormal results with you in relation to your symptoms and medical history.
The test results do not indicate how severe the cystic fibrosis is. The test only shows if a person could have the disease.
Abnormal (high) values
High values:
- Usually mean a person has cystic fibrosis. Some people with cystic fibrosis have borderline or even normal sweat chloride levels.
- May be caused by other conditions. But the sweat test is
not used to diagnose these conditions, which include:
- Adrenal gland problems, such as adrenal insufficiency or Addison's disease.
- Hypothyroidism.
- Kidney failure.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- A baby's age. Babies younger than 4 weeks may not produce enough sweat to give reliable test results and may have lower sweat chloride levels than older babies and children. A minimum amount of sweat is needed for accurate test results regardless of the child's age.
- A skin rash or sore on the area of the skin where the gauze pads are attached.
- Acute or severe illness.
- Dehydration or heavy sweating.
- Decreased sweating.
- Normal fluctuations in sodium and chloride during puberty.
- A decrease in the hormone aldosterone.
- Steroid medicines, such as fludrocortisone.
WebMD Medical Reference from Healthwise
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