An NHS trust has sent letters to more than 500 women who had cervical smear tests taken by a nurse who may not have been suitably qualified.
Health chiefs at Eastern and Coastal Kent NHS Trust invited the 536 affected women to have their tests repeated after identifying an issue with the qualifications of a nurse to take the tests.
The tests were performed in GP surgeries in Sheppey and Sittingbourne, Kent, over a two-year period from April 2007.
Although the nurse attended theoretical and practical sessions, the assessment was not independently examined and final authorisation was not given.
However, Dr John Rodriguez, assistant director of public health and screening lead for Kent and Medway, said there was no evidence to suggest that the tests carried out by the nurse were of a poor quality and the laboratory results appear to show what would be expected.
"We would like to apologise for any distress or inconvenience this may cause," he added. "Although it is most likely that the tests were performed to a satisfactory standard, we cannot be sufficiently certain, and therefore this recall exercise is a precautionary measure."