The Variation in IRT in Different Ethnic Groups in England-Implications for a Newborn Screening Programme for CF in Diverse Multiethnic Populations.

Increasing ethnic diversity raises potential inequalities within screening programmes. In the UK, newborns are screened for CF by initially measuring IRT. Dried blood spot IRT levels above a set cut-off require follow-up testing to establish a screening result. Variation exists in IRT levels between different ethnicities and therefore impacts the number of potentially false positive results obtained from ethnic groups. Over a 4-year period, IRT data was collected, and the 99.5th centile was calculated for different ethnic groups. Significant differences were noticed between ethnic groups, and the CF outcome data over a 10-year period were then analysed to establish the effect this had on positive predictive values. The largest difference in IRT 99.5th centile values was seen between the White British and Black African groups. Positive predictive values for Black African and Indian ethnic groups were much lower than the other groups. Rather than try to incorporate ethnicity into the UK CF screening algorithm, we suggest making CF clinicians aware of the differences between different ethnic groups to inform counselling families who receive screen-positive results.