Although cystic fibrosis (CF) is the most common, life-threatening autosomal recessive genetic disorder of the white population, there are often delays in diagnosis and hence start of treatment. Advances of the past two decades have made CF screening feasible using routinely collected neonatal blood specimens and measuring an enzyme level followed by CF mutation DNA analysis. Our overall goal of the study is to see if early diagnosis of CF through neonatal screening will be medically beneficial without major risks. ''Medically beneficial'' refers to better nutrition and/or pulmonary status, whereas '' risks'' include laboratory errors, miscommunication or misunderstanding, and adverse psychosocial consequences. Specific aims include assessment of the benefits, risks, costs, quality of life, and cognitive function associated with CF neonatal screening and a better understanding of the epidemiology of CF.

A comprehensive, randomized clinical trial emphasizing early diagnosis as the key variable has been underway since 1985. Nutritional status has been assessed using height and weight measurements and biochemical methods. The results have demonstrated significant benefits in the screened (early diagnosis) group. We are now focusing on the effect of early diagnosis of CF on pulmonary outcome. Pulmonary status is measured using chest radiographs, chest scans using high resolution computerized tomography, and pulmonary function tests. Other factors that we are looking at include risk factors for the acquisition of respiratory pathogens such as Pseudomonas aeruginosa, quality of life and cognitive function of children with CF who underwent early versus delayed diagnosis, as well as the cost effectiveness of screening and the costs of diagnosis and treatment of CF throughout childhood.

If the questions underlying this study are answered favorably, it is likely that neonatal screening using a combination of enzyme level (immunoreactive trypsinogen) and DNA test will become the routine method for identifying new cases of CF not only in the State of Wisconsin, but throughout the country.

Inclusion Criteria:

• Must have been born in the State of Wisconsin
• Must have been born between April 15, 1985 and June 30, 1994
• Must have had a valid newborn screening test for cystic fibrosis in the first 28 days of life.
• Must have a sweat chloride test greater or equal to 60 mmol/Liter
• Parental consent