Reexamining the Minimum Sweat Rate Requirement for Sweat Chloride Testing

Area of Science:

• Clinical Chemistry
• Diagnostic Testing
• Pediatric Medicine

Background:

• Sweat chloride testing is crucial for diagnosing cystic fibrosis (CF).
• Current guidelines mandate a minimum sweat rate for reliable results.
• Failure to meet this rate (quantity not sufficient, QNS) necessitates test re-collection.

Purpose of the Study:

• To investigate the correlation between sweat rate and sweat chloride concentration ([Cl-]).
• To evaluate the accuracy of sweat specimens collected below the minimum rate.
• To explore the utility of pooling bilateral specimens for chloride measurement.

Main Methods:

• Pearson correlation analyzed sweat rate vs. [Cl-] in 674 macroduct collections.
• Weighted kappa assessed CF diagnostic concordance for discordant sweat rates.
• Deming regression compared [Cl-] in pooled vs. neat bilateral specimens.

Main Results:

• A negligible correlation (r = -0.0735) was found between sweat rate and [Cl-].
• Substantial agreement in CF diagnostic classification was observed despite discordant sweat rates.
• Pooled specimens showed high concordance with neat specimens (slope=0.984, intercept=0.796).

Conclusions:

• The minimum sweat rate for macroduct collectors may be unnecessarily stringent.
• Reporting results from specimens with lower sweat rates (≥0.3 µL/min) may decrease QNS rates.
• Pooling bilateral sweat collections appears feasible for achieving adequate sample volume.