Molecular genetic testing for cystic fibrosis: Laboratory performance on the College of American Pathologists external proficiency surveys

Background: Molecular testing for cystic fibrosis mutations is widespread and routine in reproductive decision making and diagnosis. Our objective was to assess the level of performance of laboratories for this test. Methods: The College of American Pathologists administers external proficiency testing with multiple DNA samples distributed biannually. Results are analyzed, reviewed, and graded by the joint College of American Pathologists/American College of Medical Genetics and Genomics Biochemical and Molecular Genetics Committee. Assessment is based on genotype and associated clinical interpretation. Results: Overall, 357 clinical laboratories participated in the proficiency testing survey between 2003 and 2013 (322 in the United States and 35 international). In 2013, US participants reported performing nearly 120,000 tests monthly. Analytical sensitivity and specificity of US laboratories were 98.8% (95% confidence interval: 98.4-99.1%) and 99.6% (95% confidence interval: 99.4-99.7%), respectively. Analytical sensitivity improved between 2003 and 2008 (from 97.9 to 99.3%; P = 0.007) and remained steady thereafter. Clinical interpretation matched the intended response for 98.8, 86.0, and 91.0% of challenges with no, one, or two mutations, respectively. International laboratories performed similarly. Discussion: Laboratory testing for cystic fibrosis in the United States has improved since 2003, and these data demonstrate a high level of quality. Neither the number of samples tested nor test methodology affected performance.