Abstract
BackgroundTo assess the quality of sweat test (ST) based on the proportion of sweat sodium and sweat chloride as diagnostic parameter of cystic fibrosis (CF).MethodsA retrospective study of 5,721 sweat samples and subsequent descriptive analysis were carried out. The test was considered “of good quality” (correct) when: (i) sweat chloride was lower than 60 mEq/L, and sweat sodium was higher than sweat chloride; (ii) sweat chloride was higher than 60 mEq/L, and sweat sodium was lower than sweat chloride.ResultsThe study included 5,692/5,721 sweat samples of ST which had been requested due to clinical presentations compatible with CF and/or neonatal screenings with altered immunoreactive trypsinogen values. Considering the proportion of sweat sodium and sweat chloride as ST quality parameter, the test was performed correctly in 5,023/5,692 (88.2 %) sweat samples. The sweat chloride test results were grouped into four reference ranges for chloride (i) chloride < 30 mEq/L: 3,651/5,692 (64.1 %); (ii) chloride ≥ 30 mEq/L to < 40 mEq/L: 652/5,692 (11.5 %); (iii) ≥ 40 mEq/L to < 60 mEq/L: 673/5,692 (11.8 %); (iv) ≥ 60 mEq/L: 716/5,692 (12.6 %). In the comparative analysis, there was no association between ST quality and: (i) symptoms to indicate a ST [respiratory (p = 0.084), digestive (p = 0.753), nutritional (p = 0.824), and others (p = 0.136)], (ii) sweat weight (p = 0.416). However, there was a positive association with: (i) gender, (ii) results of ST (p < 0.001), (iii) chloride/sodium ratio (p < 0.001), (iv) subject’s age at the time of ST [grouped according to category (p < 0.001) and numerical order (p < 0.001)]. For the subset of 169 patients with CF and two CFTR mutations Class I, II and/or III, in comparative analysis, there was a positive association with: (i) sweat chloride/sodium ratio (p < 0.001), (ii) sweat chloride values (p = 0.047), (iii) subject’s age at the time of the ST grouped by numerical order (p = 0.001).ConclusionsConsidering that the quality of ST can be assessed by levels of sweat sodium and sweat chloride, an increasing number of low-quality tests could be observed in our sweat samples. The quality of the test was associated with important factors, such as gender, CF diagnosis, and subjects’ age.
Highlights
To assess the quality of sweat test (ST) based on the proportion of sweat sodium and sweat chloride as diagnostic parameter of cystic fibrosis (CF)
The ST was considered “of good quality” when: (i) sweat chloride was lower than 60 mEq/L, and sweat sodium was higher than sweat chloride in subjects without CF; (ii) sweat chloride was higher than 60 mEq/L, and sweat sodium was lower than sweat chloride in patients with CF (Fig. 1)
3,023 sweat samples collected from males (53.3 %) and 2,652 (46.7 %) sweat samples collected from females were included and analyzed
Summary
To assess the quality of sweat test (ST) based on the proportion of sweat sodium and sweat chloride as diagnostic parameter of cystic fibrosis (CF). The sweat test (ST) is considered the gold standard for the diagnosis of cystic fibrosis (CF) [1]. There are only a few quality parameters to perform ST. Increased chloride values observed in ST are due to mutations in the CFTR gene (Cystic Fibrosis Transmembrane Conductance Regulator), which encodes a protein with the same name [3]. A conclusive diagnosis of CF can be made with the identification of two mutations in the CFTR gene [4, 5]. It is not always possible to conduct genetic tests and perform complete CFTR gene sequencing for all patients, due to high costs and/or technical limitations. ST has been widely used as a tool for the diagnosis of CF for over 50 years
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