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Sweat conductivity for diagnosing cystic fibrosis after positive newborn screening: prospective, diagnostic test
Renata Marcos Bedran1, Cristina Gonçalves Alvim1, Olívia Gonçalves Sader1
1Faculty of Medicine, Department of Pediatrics, and Cystic Fibrosis Clinic, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Insights
Sweat conductivity accurately diagnoses cystic fibrosis (CF) in newborns. This diagnostic test shows high sensitivity and specificity, effectively ruling in or out CF in infants.
Area of Science:
- Neonatal screening
- Diagnostic test accuracy
- Pediatric pulmonology
Background:
- Cystic fibrosis (CF) screening in newborns is crucial for early intervention.
- Accurate diagnostic tools are essential for confirming CF in infants.
- Two-tiered immunoreactive trypsinogen testing is a common initial screening method.
Purpose of the Study:
- To evaluate the diagnostic accuracy of sweat conductivity (SC) in newborns and young infants.
- To compare SC performance against sweat chloride testing for CF diagnosis.
- To determine the utility of SC in confirming or excluding CF after positive newborn screening.
Main Methods:
- Prospective, population-based diagnostic accuracy study.
- Simultaneous sweat conductivity and sweat chloride measurements in 1193 infants.
- Analysis of sensitivity, specificity, predictive values, and likelihood ratios for SC.
Main Results:
- Sweat conductivity demonstrated high accuracy with 98.5% sensitivity and 99.9% specificity.
- Overall accuracy was 99.8%, with positive predictive value of 98.5% and negative predictive value of 99.9%.
- Positive SC results increased CF probability 350-fold; negative results reduced it to near zero.
Conclusions:
- Sweat conductivity is a highly accurate test for diagnosing cystic fibrosis in newborns and young infants.
- SC effectively rules in or rules out CF in infants with positive two-tiered immunoreactive trypsinogen results.
- The findings support the use of sweat conductivity as a reliable diagnostic tool in neonatal CF screening programs.
Objective:
To assess the accuracy of sweat conductivity among newborns and very young infants.
Design:
Prospective, population-based, diagnostic test accuracy study.
Setting:
Public Statewide Newborn Screening Programme where the incidence rate of cystic fibrosis (CF) is ≈1:11 000.
Patients:
Newborns and very young infants with positive two-tiered immunoreactive trypsinogen.
Interventions:
Sweat conductivity and sweat chloride were performed simultaneously, on the same day and facility by independent technicians, with the cut-off values of 80 mmol/L and 60 mmol/L, respectively.
Main Outcome Measures:
Sensitivity, specificity, positive and negative predictive values (PPV and NPV), overall accuracy, positive and negative likelihood ratios (+LR, -LR) and post (sweat conductivity (SC)) test probability were calculated to assess SC performance.
Results:
1193 participants were included, 68 with and 1108 without CF, and 17 with intermediate values. The mean (SD) age was 48 (19.2) days, ranging from 15 to 90 days. SC yielded sensitivity of 98.5% (95% CI 95.7 to 100), specificity of 99.9% (95% CI 99.7 to 100), PPV of 98.5% (95% CI 95.7 to 100) and NPV of 99.9% (95% CI 99.7 to 100), overall accuracy of 99.8% (95% CI 99.6 to 100), +LR of 1091.7 (95% CI 153.8 to 7744.9) and -LR of 0.01 (95% CI 0.00 to 0.10). After a positive and negative sweat conductivity result, the patient's probability of CF increases around 350 times and drops to virtually zero, respectively.
Conclusion:
Sweat conductivity had excellent accuracy in ruling in or ruling out CF after positive two-tiered immunoreactive trypsinogen among newborns and very young infants.
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