How to perform and interpret the sweat test

Abstract

Cystic fibrosis (CF) is the most common life-threatening autosomal-recessive disease affecting Caucasians in the western world. The sweat test is the main diagnostic test for CF. It is indicated as part of the clinical assessment for infants that have picked up on the national neonatal screening programme. It may also be requested where clinical suspicion of a diagnosis of CF exists despite normal screening results. This article outlines the physiological basis behind sweat testing and the technical aspects of performing the test. Indications for performing the test are also considered. The article aims to provide clinicians with a guide to interpretation of results.

Sweat Testing and Recent Advances

“…The cutoff value for sweat Cl − testing is the same regardless of a patient's age ( 7 , 28 ). A level of Cl − of higher than 60 mmol/L in the sweat is indicative of CF; concentrations lower than 30 mmol/L are considered normal, and CF is unlikely.…”

Research advances in molecular mechanisms underlying the pathogenesis of cystic fibrosis: From technical improvement to clinical applications (Review)

“…As varying molecular subtypes are associated with different phenotypes, experts from the 'Cystic Fibrosis Foundation' convened a panel of criteria for diagnosing CF in 1996 (81,82). Several tests, including the sweat test (83,84), nasal potential difference (NPD) (85)(86)(87), DNA screening (88,89) and a ciliary test, were recommended. The current review discussed traditional (regular) approaches (sweat test and NPD measurement) and novel methods.…”

“…The sweat test is an effective method for detecting CF, covering all age ranges (83,84). However, the application of creams and lotions within 1 day prior to sweat collection can disrupt the precision of diagnosis.…”

“…Collection of a sufficient volume of sweat is required for laboratory assays, through which Na and Clconcentrations are determined. Incorrect results occur due to contamination, evaporation, insufficient sample and technical errors (83,84).…”

The Italian External Quality Assessment Program for Cystic Fibrosis Sweat Chloride Test: Does Active Participation Improve the Quality?

“…Rarely, a sweat test returns normal results in a patient with two identified CF-causing mutations [12][13][14] since the CFTR protein's main function consists of transporting chloride ions in and out of the cell. In a sweat gland, defective CFTR proteins result in the impaired reabsorption of chloride ions and high levels of chloride in sweat [15].…”