Tests
1st tests to order
sweat test
Test
If suspected (i.e., patient presents with symptoms/signs or a positive family history), a sweat test (pilocarpine iontophoresis test) should be performed.
A positive sweat test (sweat chloride ≥60 mEq/L) suggests CF and requires immediate referral to a CF center.
A negative sweat test (sweat chloride <30 mEq/L) suggests that CF is unlikely.[28]
An intermediate sweat test (sweat chloride 30-59 mEq/L) requires CFTR genetic analysis.
Sweat tests may be performed in children of any age. Some children may not produce enough sweat to give accurate results. If this occurs, the child should be retested within a week.
Result
positive (sweat chloride ≥60 mEq/L)
genetic testing
Test
Most laboratories will perform an initial "screen" for the most common CFTR mutations. If two common mutations are not found, most laboratories have an option for sequencing more of the CFTR gene or the entire CFTR gene.
In individuals with sweat test results that fall within the intermediate range (defined as a sweat chloride measurement of 30-59 mEq/L), it remains crucial to evaluate further with a CFTR genetic analysis. Subsets of these patients can be characterized as having CFTR-related metabolic syndrome (CRMS), also known as a CF screen-positive, inconclusive diagnosis (CFSPID) in Europe.
If there are existing genetic test results, do not order a duplicate test unless there is uncertainty about the existing result, e.g., the result is inconsistent with the patient’s clinical presentation or the test methodology has changed.[31]
Result
CF is diagnosed in the presence of two disease-causing mutations
Tests to consider
sinus imaging
Test
CF is associated with increased risk for nasal polyps and rhinosinusitis. Nasal endoscopy and/or CT may be considered. Sinus imaging is not a specific test for CF.
Result
may show pansinusitis; nasal polyposis
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