Objectives: To document the relevance of sweat potassium concentration in a reported case of a white Caucasian 27-month-old boy who presented with non-specific respiratory symptoms and several abnormal sweat test results compatible with cystic fibrosis (CF).
Design and methods: Repeated sweat tests using the Gibson-Cooke technique in the presence and absence of the mother.
Results: The high within- and between-test variability, the very low sweat potassium concentrations, several aspects of the family's history and a negative exhaustive genetic analysis to identify any CFTR mutation, raised suspicion for pediatric condition falsification. Two additional sweat tests performed in the absence of the mother were normal.
Conclusion: CF diagnosis was then discarded and a Munchausen syndrome by proxy diagnosis was proposed.