Sweat chloride testing in infants identified as heterozygote carriers by newborn screening.

The reference ranges for sweat [C1(-)] were reevaluated in 300 infants referred to our Center as carriers of at least 1 cystic fibrosis mutation identified through newborn screening. The recommended borderline range of 30 to 59 mmol/L failed to identify all individuals who were compound heterozygotes. Our data support using a borderline range of 24 to 59 mmol/L.