The sweat test is recognized as the most reliable diagnostic method for cystic fibrosis (CF).
Understanding the Sweat Test for Cystic Fibrosis
The sweat test, formally known as the quantitative pilocarpine iontophoresis sweat test, stands as the gold standard for diagnosing cystic fibrosis. It is a straightforward, painless, and highly accurate procedure that measures the concentration of chloride (a component of salt) in a person's sweat. Individuals with CF typically exhibit higher levels of chloride in their sweat due to a defect in the CFTR protein, which regulates the movement of salt and water in and out of cells.
When is a Sweat Test Recommended?
A sweat test is commonly recommended in several key situations:
- Positive Newborn Screening: If a baby's initial screening test suggests the possibility of CF.
- Presence of Symptoms: When an individual, whether a child or an adult, displays symptoms frequently associated with cystic fibrosis. These can include:
- Persistent coughing
- Recurrent lung infections
- Poor weight gain despite adequate food intake
- Skin that tastes unusually salty
- Greasy, bulky stools
- Family History: If there is a known family history of cystic fibrosis.
How the Sweat Test Works
The procedure for a sweat test is simple and generally takes about an hour from start to finish, though the sweat collection itself is much shorter:
- A small, colorless chemical called pilocarpine is applied to a tiny area of the skin, typically on the forearm or thigh.
- A mild electrical current is then used to stimulate the sweat glands to produce sweat. This process, known as iontophoresis, causes a tingling sensation but is not painful.
- Sweat is collected on a piece of filter paper or in a small coil for approximately 30 minutes.
- The collected sweat sample is sent to a laboratory to accurately measure its chloride concentration.
Interpreting Sweat Test Results
Results are usually available within a few days. Chloride levels are measured in millimoles per liter (mmol/L) and are interpreted as follows:
| Chloride Level (mmol/L) | Interpretation |
|---|---|
| < 30 | Negative for CF |
| 30-59 | Intermediate/Borderline (further testing, such as genetic testing, may be needed) |
| ≥ 60 | Positive for CF |
It is crucial that sweat tests are performed at a CF Foundation-accredited care center to ensure the highest level of accuracy and reliability. These specialized centers possess the necessary equipment and trained personnel to conduct the test correctly and interpret the results within the context of a CF diagnosis. For more detailed information about cystic fibrosis and its diagnostic procedures, you can visit the Cystic Fibrosis Foundation website.
