What sweat chloride result is diagnostic of cystic fibrosis (CF) in children?

The sweat chloride test is a critical diagnostic tool for cystic fibrosis (CF) in children. A result of ≥60 Eq/L in at least two measurements is considered diagnostic of cystic fibrosis. This threshold is based on the understanding that cystic fibrosis affects the CFTR gene, leading to abnormal chloride transport across epithelial cells and resulting in elevated chloride levels in sweat.

In the context of cystic fibrosis, a sweat chloride level of 60 Eq/L or higher indicates significant disruption in ion transport, which is consistent with the pathology of the disease. Values at or above this level are used as a guideline to confirm a diagnosis of CF. It is important for clinical decisions that the measurement is repeated, as sweat test values can vary, and confirmation with at least two tests ensures reliability and accuracy in diagnosing the condition.

The other options either present lower thresholds, which may not indicate CF reliably, or a single measurement which lacks the confirmatory aspect needed for a proper diagnosis.