CLSI’s document provides revised guidelines for screening cystic fibrosis

Clinical and Laboratory Standards Institute (CLSI) recently published Sweat Testing: Sample Collection and Quantitative Chloride Analysis; Approved Guideline—Third Edition (C34-A3). This document addresses appropriate methods of collection and analysis, quality control, and the evaluation and reporting of sweat test results for the diagnosis of cystic fibrosis.

“This updated version of C34 is very timely because now all 50 states have mandatory newborn screening for cystic fibrosis. The new material included in the revised guidelines will be a valuable resource for laboratories performing sweat chloride testing for the confirmation of cystic fibrosis.”

The quantitative measurement of chloride in sweat (commonly called the “sweat test”) is used to confirm the diagnosis of cystic fibrosis (CF). CF is the most common life-threatening genetic disease within the white population. It is an autosomal recessive disorder characterized by viscous secretions that affect the exocrine glands, primarily in the lungs and pancreas. Patients with CF have an increased concentration of sodium, chloride, and potassium in their sweat.

Vicky A. LeGrys, DrA, MT(ASCP), University of North Carolina School of Medicine, and chairholder of the committee that developed the document, says, “This updated version of C34 is very timely because now all 50 states have mandatory newborn screening for cystic fibrosis. The new material included in the revised guidelines will be a valuable resource for laboratories performing sweat chloride testing for the confirmation of cystic fibrosis.”

The following items are new in this edition:

• Microvolume procedure for sweat chloride analysis
• Method validation for sweat chloride
• Quality assurance for sweat collection
• Reference ranges for infants and beyond infancy

Because the sweat test has been reported to have unacceptably high false-positive and false-negative rates attributable to inaccurate methodology, technical error, and patient physiology, comprehensive guidelines addressing the collection of sweat and the quantitative measurement of chloride in sweat are needed. This document describes in detail the quantitative pilocarpine iontophoresis test for the determination of sweat chloride, including techniques to minimize the potential for false-positive and false-negative test results.

The primary audience includes laboratory and clinical personnel responsible for collecting, analyzing, reporting, and evaluating sweat test results. Sample pages can be previewed on CLSI’s website.