Role of sweat ion ratios in diagnosing cystic fibrosis.

Sweat chloride (Cl ) concentration is the gold standard for diagnosing cystic fibrosis (CF). This is, however, challenging among patients with borderline values. Previous studies have reported that the sweat Cl /Na ratio may be useful for diagnosing CF; however, little is known about Cl /K and (Cl  + Na )/K ratios.