Laboratory tests for the diagnosis of cystic fibrosis.

Cystic fibrosis (CF) remains the most common life-limiting inherited disease in America. Making an accurate, early diagnosis is essential to the management of the disease. The diagnostic criteria for CF require the presence of 1 or more typical clinical features, a family history of CF, or a positive newborn screening test, plus laboratory evidence of the CF transmembrane conductance regulator (CFTR) dysfunction. In the past, the laboratory test of abnormal CFTR function was based largely on an elevated sweat chloride test result. The recent development of a genotypic CFTR mutation screen has greatly improved diagnostic accuracy. Increased screening of the CFTR locus has led to the recognition of a number of atypical CF disorders. Recently, a 2-tiered newborn screening protocol including CFTR genotyping has become popular, increasing the likelihood of early diagnosis.