The national data opt-out (NDOO) was introduced on 25 May 2018 following recommendations from the National Data Guardian and indicates that a patient does not want their confidential patient information to be shared for purposes beyond their individual care across the health and care system in England. The mandatory implementation deadline of the NDOO was 31 July 2022. The change involved treating patients as opted out nationally rather than locally. In terms of the opt-out process, any patient that had a type 2 opt-out recorded on a GP system on or before 11 October 2018 then had it automatically converted to a NDOO on implementation (in 2022).
Based on discussions with GP software suppliers, our understanding is that the technical implementation of the NDOO requires new format NHS numbers, which were introduced in 1995-96. As a result, primary care data for patients in England with an old format NHS number or a missing NHS number is no longer shared with CPRD and no longer appears in CPRD Aurum and GOLD databases. This particularly affects patients in England who died or transferred out of a participating practice before they were issued a new NHS number, i.e. before 1997. We are liaising with the NDOO Implementation team to verify this and explore whether there is a way to receive the data for these patients who have not otherwise registered an opt-out.
In the meantime, researchers should be aware of this issue, and should consider excluding time before 1997 when defining a study period.