A reference interval for sweat chloride in infants aged between five and six weeks of age

Area of Science:

• Pediatric diagnostics
• Newborn screening
• Cystic Fibrosis (CF) diagnostics

Background:

• Establishing reference intervals for sweat chloride in infants is vital for cystic fibrosis (CF) newborn screening.
• The study focuses on infants aged 5-6 weeks, a critical period for CF diagnosis.
• Comparison of the gold standard quantitative pilocarpine iontophoresis (QPIT) with the emerging Macroduct method was performed.

Purpose of the Study:

• To establish a reference interval for sweat chloride in infants without CF.
• To compare the QPIT (coulometry) method with the Macroduct (ISE) system for sweat collection and analysis.
• To assess the validity of the Macroduct system in infants aged 5-6 weeks.

Main Methods:

• Prospective study involving healthy infants at 5-6 weeks of age.
• Simultaneous sweat collection using QPIT and Macroduct systems on the outer thighs.
• Analysis of sweat chloride concentrations via flame photometry, coulometry (QPIT), and ion-selective electrodes (Macroduct).

Main Results:

• A 92% success rate was achieved for consecutive sweat collections.
• Sweat chloride concentrations were normally distributed with excellent agreement between methods.
• Median sweat chloride was 11.2 mmol/L (IQR 8-13) with QPIT (coulometry); the 99.5th centile was 24 mmol/L.

Conclusions:

• The Macroduct (ISE) capillary sweat collection system is validated for use in this infant age group.
• Sweat chloride levels exceeding 30 mmol/L warrant further assessment in a specialist CF center.
• This supports the use of Macroduct as a reliable method in neonatal CF screening programs.