CFTR and cystic fibrosis: During the same time period, 189,857 infants born in Indiana underwent NBS for CF and had no identified CFTR variants, i.e., infants with an IRT not in the top 4% for the day, or in the top 4% for the day but with no CFTR variants identified, and were not diagnosed with CF through other means, e.g., meconium ileus.