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J Cyst Fibros. 2014 Sep;13(5):528-33. doi: 10.1016/j.jcf.2014.01.002. Epub 2014 Jan 31.

Sweat conductivity: an accurate diagnostic test for cystic fibrosis?

Author information

1
Pediatric Pulmonology Division, Instituto da Criança, Hospital das Clínicas, University of São Paulo, Av. Dr. Enéas Carvalho de Aguiar, 647, cep 05403-900 São Paulo - SP - Brazil. Electronic address: anacmattar@uol.com.br.
2
Department of Maternal and Child Health, College of Public Health, University of Sao Paulo, Av. Dr. Arnaldo, 715, cep 01246-904 São Paulo - SP - Brazil. Electronic address: leone.claudio@gmail.com.
3
Pediatric Pulmonology Division, Instituto da Criança, Hospital das Clínicas, University of São Paulo, Av. Dr. Enéas Carvalho de Aguiar, 647, cep 05403-900 São Paulo - SP - Brazil. Electronic address: jocarod@uol.com.br.
4
Pediatric Pulmonology Division, Instituto da Criança, Hospital das Clínicas, University of São Paulo, Av. Dr. Enéas Carvalho de Aguiar, 647, cep 05403-900 São Paulo - SP - Brazil. Electronic address: fabiola.adde@outlook.com.

Abstract

BACKGROUND:

Sweat chloride test is the gold standard test for cystic fibrosis (CF) diagnosis. Sweat conductivity is widely used although still considered a screening test.

METHODS:

This was a prospective, cross-sectional, diagnostic research conducted at the laboratory of the Instituto da Criança of the Hospital das Clínicas, São Paulo, Brazil. Sweat chloride (quantitative pilocarpine iontophoresis) and sweat conductivity tests were simultaneously performed in patients referred for a sweat test between March 2007 and October 2008. Conductivity and chloride cut-off values used to rule out or diagnose CF were <75 and ≥90 mmol/L and <60 and ≥60 mmol/L, respectively. The ROC curve method was used to calculate the sensitivity, specificity, positive (PPV) and negative predictive value (NPV), as well as the respective 95% confidence intervals and to calculate the area under the curve for both tests. The kappa coefficient was used to evaluate agreement between the tests.

RESULTS:

Both tests were performed in 738 children, and CF was ruled out in 714 subjects; the median sweat chloride and conductivity values were 11 and 25 mmol/L in these populations, respectively. Twenty-four patients who had received a diagnosis of CF presented median sweat chloride and conductivity values of 87 and 103 mmol/L, respectively. Conductivity values above 90 mmol/L had 83.3% sensitivity, 99.7% specificity, 90.9% PPV and 99.4% NPV to diagnose CF. The best conductivity cut-off value to exclude CF was <75 mmol/L. Good agreement was observed between the tests (kappa: 0.934).

CONCLUSIONS:

The sweat conductivity test yielded a high degree of diagnostic accuracy and it showed good agreement with sweat chloride. We suggest that it should play a role as a diagnostic test for CF in the near future.

KEYWORDS:

Conductivity; Cystic fibrosis; Pilocarpine; Sweat test

PMID:
24485874
DOI:
10.1016/j.jcf.2014.01.002
[Indexed for MEDLINE]
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