Cystic fibrosis laboratory tests

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Overview

A multitude of tests is used to identify complications of CF and to monitor disease progression.

Laboratory Findings

Cystic fibrosis may be diagnosed by many different categories of testing including those such as, newborn screening, sweat testing, or genetic testing. As of 2006 in the United States, 10 percent of cases are diagnosed shortly after birth as part of newborn screening programs. The newborn screen initially measures for raised blood concentration of immunoreactive trypsinogen. However, most states and countries do not screen for CF routinely at birth. Therefore, most individuals are diagnosed after symptoms prompt an evaluation for cystic fibrosis. The most commonly-used form of testing is the sweat test. Sweat-testing involves application of a medication that stimulates sweating (pilocarpine) to one electrode of an apparatus and running electric current to a separate electrode on the skin. This process, called iontophoresis, causes sweating; the sweat is then collected on filter paper or in a capillary tube and analyzed for abnormal amounts of sodium and chloride. People with CF have increased amounts of sodium and chloride in their sweat. CF can also be diagnosed by identification of mutations in the CFTR gene. Examination of the sputum under a microscope is used to identify which bacteria are causing infection so that effective antibiotics can be given. Blood tests can identify liver problems, vitamin deficiencies, and the onset of diabetes.