Diagnostic Investigation for Cystic Fibrosis

Cystic Fibrosis (CF) is a genetic disorder that affects the exocrine glands. The most definitive diagnostic investigation involves measuring the concentration of chloride in a patient's sweat.

Key Diagnostic Test

• High sweat chloride content: This is the hallmark diagnostic test for Cystic Fibrosis. In individuals with CF, the transport of chloride ions across epithelial cells is impaired due to mutations in the CFTR gene. This leads to an abnormally high concentration of chloride in their sweat. A sweat chloride level above a certain threshold (typically 60 mEq/L) is considered diagnostic, especially when confirmed by repeat testing.

Evaluating Other Options

• Deficiency of the enzyme mucinase: While mucus is a key feature affected in CF, mucinase deficiency is not the primary diagnostic marker.
• Alpha-1 aldolase deficiency: This enzyme deficiency is related to hereditary fructose intolerance, not Cystic Fibrosis.
• Increased copper excretion in urine: Elevated urinary copper is typically associated with Wilson's disease, a disorder of copper metabolism.

Therefore, a high sweat chloride content is the investigation that is diagnostic of Cystic Fibrosis.