Sweat potassium concentration may help to identify falsification of sweat test: a case report

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).

Repeated sweat tests using the Gibson-Cooke technique in the presence and absence of the mother.

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.

CF diagnosis was then discarded and a Munchausen syndrome by proxy diagnosis was proposed.