Did You Know?
We may be carriers of certain conditions (not have the condition but possess the ability to pass it to the next generation). Learn more:
What Is A Cystic Fibrosis Sweat Test?
Cystic fibrosis is an inherited genetic disease that affects nearly 30,000 children and adults in the USA.
The development of thick, sticky mucus build-up in organs characterizes this condition.
Diagnosing cystic fibrosis early helps effectively manage the condition and improves the individual’s quality of life.
The cystic fibrosis sweat test helps determine if an individual has this condition by assessing the amount of chloride in their sweat.
Why Is The Test Done?
The sweat chloride test is the gold standard for diagnosing cystic fibrosis.
How Does The Test Work?
In people with cystic fibrosis, there is a problem with the movement of chloride ions across cell membranes.
This means there is a higher concentration of salt in sweat when compared with people who do not have cystic fibrosis.
The sweat chloride test can be performed as early as 48 hours after birth.
It is recommended for babies with a family history of the condition or those who tested positive for cystic fibrosis in the newborn screening test.
Details Of The Sweat Test Procedure
The chloride sweat test is a simple procedure that takes about 30 minutes.
Preparation
No special preparation is required for the cystic fibrosis sweat test.
You can allow your child to eat, drink and continue their routine.
However, avoiding lotions on the skin for 24 hours before the test is recommended.
How Do I Prepare My Child For A Sweat Test?
Since no needles are used in this sweat test, you can rest assured that your child will be comfortable throughout the test duration.
The test usually takes around 30 minutes but may take longer in some cases. Bring a few books or toys to entertain your child during the test.
Procedure
The chloride sweat test is simple and usually involves the following steps:
- The part of the skin where the test is decided to be performed is cleaned with water.
- Two gels or special pads containing Pilocarpine (a substance that makes the skin sweat) are applied to the cleaned area.
- To ensure Pilocarpine is absorbed, the skin is stimulated by a small current from a battery for around five minutes.
- This may produce a tingling sensation but does not harm or hurt your child.
- Once the skin has been stimulated, the applied gel and pads are removed, and the skin is cleaned.
- The sweat is collected on filter paper, gauze, or a plastic coil. This step takes around 30 minutes.
- The collected sweat sample is sent to a laboratory for testing.
The area on the arm or leg that was used for the rest may remain red for a few hours, but there is nothing to worry about.
Can The Sweat Test Be Administered More Than Once?
The chloride sweat test may need to be repeated in the following scenarios:
- Not enough sweat was collected
- There was some contamination in the collected sample
- When there was a borderline chloride result
Understanding Cystic Fibrosis Sweat Test Results
Cystic fibrosis test results may take a few days to arrive. Confirm the timeline when booking the sweat test.
Chloride in sweat is measured in mmol/L (millimoles per liter)
- Chloride level of 60 mmol/L: Strong indication for cystic fibrosis
- Chloride level of 30 to 59 mmol/L: Borderline result and a repeat sweat test may be ordered
- Chloride level less than 29 mmol/L: The individual is unlikely to be diagnosed with cystic fibrosis.
So, having a sweat chloride level over 60 millimoles per liter is considered abnormal and may indicate cystic fibrosis.
The doctor will perform other tests and symptomatic assessments to confirm a cystic fibrosis diagnosis.
Factors That May Affect The Result
False positive results are rare in the case of a sweat chloride test.
However, some conditions that may falsely increase sweat chloride levels include:
- Faulty testing technique
- Atopic dermatitis
- Untreated adrenal insufficiency
- Hypothyroidism
- Malnutrition
- Pan hypopituitarism
- Ectodermal dysplasia
How Accurate Is A Sweat Test For Cystic Fibrosis?
A sweat chloride test is accurate in around 98% of patients with cystic fibrosis.
Are There Any Risks To The Test?
Risks due to the sweat chloride test are rare.
The electrical stimulation may cause skin reddening, which resolves in a few hours.
In sporadic cases, the skin may look mildly sunburned.
How Much Does A Cystic Fibrosis Sweat Test Cost?
The cystic fibrosis sweat test costs around USD 250.
Summary
- Cystic fibrosis is an inherited genetic disease characterized by the development of thick, sticky mucus build-up in organs.
- The sweat chloride test helps diagnose cystic fibrosis in about 98% of people with this condition.
- The cystic fibrosis sweat test is a non-invasive test that does not require needles and no additional preparation.
- It is important to not apply any lotions or creams on the skin at least 24 hours before the scheduled time of the sweat test.
- Having chloride levels of 60 mmol/L or higher indicates that an individual may have cystic fibrosis.
- The sweat test may be repeated if there is insufficient sweat for testing, a faulty technique was used, or the result was borderline.
References
- https://medlineplus.gov/lab-tests/sweat-test-for-cystic-fibrosis/
- https://my.clevelandclinic.org/health/diagnostics/17856-sweat-test-for-cystic-fibrosis-cf
- https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=cystic_fibrosis_sweat
- https://www.cysticfibrosis.org.uk/what-is-cystic-fibrosis/diagnosis/the-sweat-test
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1320177/
