The acting Clinical Director of the Health Service Executive's cervical screening programme has said 6,000 women will be contacted by the end of next week and advised to return to their GPs for repeat smear tests.
Peter McKenna was speaking on RTÉ's Morning Ireland, after the HSE confirmed that it has been advised of a problem involving some samples being tested outside of the recommended timeframe.
Dr McKenna said that CervicalCheck has been informed that one part of the two-stage test is being carried out outside of the manufacturer's recommended timeframe.
He said: "What appears to have happened is that the test should be carried out within 30 days of the smear being taken.
"What appears to have happened is that the laboratories started counting the 30 days from the time the smear came into the laboratory, rather than from the time that the smear was taken in the clinic."
Mr McKenna said an investigation will take place to determine how the confusion arose, but said that the HSE's focus at the moment is on the women affected.
He said the HSE was alerted to the problem at the end of November, but said the extent of the problem unfolded throughout the month of December.
Dr McKenna confirmed that this is a separate issue to the backlog in smear tests, caused by an increase in the number of women undergoing cervical smear tests last year.
Cervical screening under the microscope once again
What is the latest CervicalCheck issue about?
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The HSE yesterday confirmed that almost 350,000 screening tests were submitted during 2018, which is an increase of 84,000 following concerns about cervical screening following the CervicalCheck audit.
Minister for Health Simon Harris has said he was made aware in December of a potential issue with the HPV testing, and that work is under way by the HSE to see if action was required.
Mr Harris met the HSE and his department today.
Last April, the minister announced that a free test would be made available to any woman who wanted one following the CervicalCheck controversy.
In the Dáil today, Tánaiste Simon Coveney said the HSE is working with Quest Laboratories to address a situation that had been identified.
Mr Coveney added: "Of the approximately 500,000 tested by Quest since 2015, the HSE has advised that some HPV tests have been informed outside of the recommended 30 day timeframe.
"I am assured this affects a small proportion, approximately 1% in total.
"There will be cases where a woman who has already had a test will be written to and requested for a retest on a precautionary basis."
He said the HSE would write to those women and their GPs next week to request that they return for a further test. It is expect that up to 6,000 women will be invited for a repeat test.
"These tests will be processed as a priority."
The HSE has said that even though some tests were done outside the 30-day window, the original results are still very reliable, Mr Coveney said.
"This is not a cause for undue concern. This is about transparency and correcting a mistake that should not have happened", he said.
He was responding to Sinn Féin's Pearse Doherty, who said it had become evident that the health service is in "constant chaos".
Mr Doherty said the latest developments around CervicalCheck will cause worry to many women.
He said that while we have been assured that the risk to women is low, it is yet another example of the incompetence in a chaotic system.
Mr Doherty said it was correct to guarantee free smear tests to women after the scandal broke, but Minister Harris should have consulted the labs first to ensure they had the capacity to deliver with the increased workload.
In relation to the HPV secondary testing, Mr Coveney said an issue has emerged in relation to one of the three labs that carry out this work and "we are now working to correct that and that is what we will continue to do".
Labour Leader Brendan Howlin said the problems with CervicalCheck indicated that something was deeply wrong with the programme.
"How much scandal can the screening programme take?" Mr Howlin asked.
"We are absolutely in favour of screening, but the problems besetting CervicalCheck programme indicates that something is deeply wrong."
Mr Howlin said these problems are further eroding confidence in screening and that people were anxious.
Mr Coveney said the Minister for Health had asked for a detailed report on the issue.
He also said Mr Harris, who is currently on paternity leave, was happy to answer questions on political accountability in the house, when he returns to work the week after next.