Sweat Chloride Test

The sweat chloride test is a diagnostic tool used to measure the amount of chloride in sweat. It is primarily used to diagnose cystic fibrosis (CF), a genetic disorder that affects the respiratory, digestive, and reproductive systems.

Procedure

The sweat chloride test involves stimulating the skin to produce sweat, which is then collected and analyzed for its chloride content. The procedure typically takes about 30 minutes to an hour to complete and involves the following steps:

• A mild electrical current is applied to a small area of skin, usually on the forearm or leg, to stimulate sweat production.
• A special paper or pad is used to collect the sweat.
• The collected sweat is then sent to a laboratory for analysis.

Interpretation of Results

The results of the sweat chloride test are interpreted as follows:

• Normal: A chloride level of less than 30 mmol/L is considered normal and rules out cystic fibrosis.
• Borderline: A chloride level between 30-59 mmol/L may indicate the need for further testing, as it can be seen in both individuals with and without CF.
• Abnormal: A chloride level of 60 mmol/L or higher is considered abnormal and indicates a high likelihood of cystic fibrosis.

Uses

The sweat chloride test is used to:

• Diagnose cystic fibrosis in individuals who are suspected of having the condition based on symptoms or family history.
• Confirm a diagnosis of CF in individuals who have already been diagnosed with the condition.
• Screen newborns for CF as part of routine newborn screening programs.

Risks and Limitations

The sweat chloride test is generally considered safe and has few risks. However, it may cause:

• Mild skin irritation or redness at the site where the electrical current was applied.
• Some discomfort or anxiety during the procedure.

The test may not be suitable for individuals with certain medical conditions, such as eczema or skin infections, and may require special precautions in these cases.

Additional Testing

In some cases, additional testing may be necessary to confirm a diagnosis of cystic fibrosis. This can include:

• Genetic testing to identify mutations in the CFTR gene.
• Chest X-rays or other imaging tests to evaluate lung function and structure.
• Pancreatic function tests to assess digestive enzyme production.