From the Guidelines
The typical lab range for sweat chloride in patients with cystic fibrosis is generally above 60 mmol/L, while in normal patients without CF, sweat chloride values are typically below 30 mmol/L, with an intermediate range of 30-59 mmol/L that may require additional testing for diagnosis. According to the most recent guideline evidence from 1, sweat chloride testing is a crucial diagnostic tool for cystic fibrosis, and values above 60 mmol/L are indicative of the disease. The evidence from 1 and 1 also supports these ranges, with 1 stating that a negative test has <30 mmol/L chloride, a borderline test 30–60 mmol/L, and a positive test >60 mmol/L, and 1 confirming that a higher amount of chloride in the sweat (>60mmol/l) compared to normal values indicates a diagnosis of CF.
Over time, sweat chloride values in treated CF patients can decrease, particularly with newer CFTR modulator therapies, as noted in the example answers. However, the most recent evidence from 1 emphasizes the importance of repeating sweat chloride testing at regular intervals, at least until age 8 years, to monitor changes in sweat chloride levels and to determine the need for continued testing.
Key points to consider include:
- Normal sweat chloride values: <30 mmol/L
- Borderline sweat chloride values: 30-59 mmol/L
- Abnormal sweat chloride values indicative of CF: >60 mmol/L
- The need for repeated sweat chloride testing in patients with CF, particularly in the context of newer therapies that may affect sweat chloride levels, as recommended by 1.
It is essential to interpret these values in the clinical context, considering the patient's specific CFTR mutations, therapy used, and overall clinical presentation, as sweat chloride testing remains valuable for diagnosis but has limitations for monitoring treatment response, as noted in the example answers and supported by the evidence from 1, 1, and 1.
From the Research
Sweat Chloride Ranges in Normal Patients and Cystic Fibrosis
- Normal sweat chloride values are typically less than 60 mmol/L, with 96% of adults having values less than 60 mEq/L and 99% having values less than 70 mEq/L 2
- In patients with cystic fibrosis, sweat chloride values are typically greater than 60 mmol/L, with the Cystic Fibrosis Foundation guidelines defining an intermediate range of 30-59 mmol/L for age > 6 months 3
- However, normal sweat chloride values do not exclude the diagnosis of cystic fibrosis, as some patients with mild manifestations of the disease may have normal sweat chloride values 4
Changes in Sweat Chloride Values Over Time in Treated Patients
- A change in sweat chloride concentration exceeding 36% may be considered a clinically significant response to cystic fibrosis transmembrane receptor targeted therapy 5
- Treatment with CFTR modulators such as lumacaftor/ivacaftor and elexacaftor/tezacaftor/ivacaftor can improve sweat chloride values, as well as pulmonary function and nutrition, in patients with cystic fibrosis 6
- The effects of treatment on sweat chloride values can vary, with some patients experiencing significant decreases in sweat chloride concentration while others may not show significant changes 5, 6