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Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Functional Assay (24-hour Sweat Chloride Screening)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of chloride in your sweat, which helps diagnose cystic fibrosis or assess its severity. It’s often used when symptoms like persistent cough, frequent lung infections, or digestive issues suggest a possible genetic condition.

Quick summary

["Sweat chloride testing is key for diagnosing cystic fibrosis and monitoring disease progression."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
38451-1
Short code
CFTR c.2789+5G>A Bld/T Ql
Synonyms
CFTR c.2789+5G>A Bld/T Ql
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
molgen
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Matters

Cystic fibrosis (CF) is a genetic disorder that affects the lungs and digestive system. It causes thick, sticky mucus to build up in these organs, leading to breathing problems and malnutrition. Sweat chloride testing is one of the primary ways doctors confirm a CF diagnosis because high levels of chloride in sweat are a hallmark of the condition.

How the Test Works

A small amount of sweat is collected from your forearm using a patch and patch test. The sweat is then analyzed to measure chloride levels. This test is typically done under controlled conditions to ensure accuracy.

What to Expect Before the Test

You may be asked to avoid certain medications or foods that could affect sweat production, such as diuretics or high-sodium diets, but this varies by facility. Bring any recent medications or questions to your healthcare provider.

What to Expect During the Test

The test involves placing a patch on your forearm to collect sweat over about 45 minutes. You’ll need to stay still and avoid touching the patch. The process is painless but may feel slightly uncomfortable due to the patch’s adhesive.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

CFTR Sweat Chloride Screening

Frequently asked questions

What does a high sweat chloride level mean?
A sweat chloride test result above 60 milliequivalents per liter (mEq/L) is strongly suggestive of cystic fibrosis. However, other conditions may cause elevated chloride levels, so further testing may be needed to confirm a diagnosis. Doctors may also use genetic testing to confirm CF if the sweat chloride test is positive.
What does a normal sweat chloride level mean?
A sweat chloride level below 40 mEq/L is generally considered normal and unlikely to indicate cystic fibrosis. However, some people with CF may have borderline results, so follow-up testing may be recommended.
How often should I get this test?
Your healthcare provider will determine how often you need this test based on your symptoms, medical history, and test results. For people diagnosed with cystic fibrosis, regular testing may be part of ongoing management to monitor disease progression and adjust treatments as needed.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy