The HSE has announced an immediate review of a computer glitch that meant that hundreds of women who underwent CervicalCheck screening were not issued with their results.
In a statement, HSE CEO Paul Reid said the review would be led by a chairperson external to the HSE and that it would be completed in a "timely manner".
The terms of reference will be made available early next week.
RTÉ News revealed yesterday that around 800 women who underwent CervicalCheck screening were not issued with their results due to what the HSE said was an IT issue at a US laboratory.
Mr Reid said: "In response to information emerging over recent days, I have decided to commission an immediate rapid review of this incident.
"This review will examine in detail how the communication process for providing results to women was planned and managed.
"I want this work to commence quickly and be completed in a timely manner, led by a chairperson external to the HSE.
"While this review is ongoing, we will continue to update the women involved as planned, and to work with Quest Diagnostics to get to the bottom of what has happened, what needs to be done to resolve these problems."
Earlier, the HSE said that it was known in February that there was a computer glitch at Quest Diagnostics laboratory in Chantilly in Virginia.
Dr Peter McKenna, Clinical Director of Women and Infants Health at the HSE, said that "elements" of the issue "only emerged to the HSE in the last ten days or so".
Speaking on RTÉ's News at One, he said: "The extent of what needs to be communicated to women is not yet currently absolutely certain."
Dr McKenna said the cytology results of the women affected were known and they had a minor degree of abnormality.
He said that in order to see whether they needed to go for colposcopy or not, an additional test for human papilloma virus (HPV) was carried out.
Dr McKenna said the 800 women had a HPV test carried out, but it transpired that the tests had been conducted using an out-of-date kit.
He said those women whose results had come back as positive had been treated, while it was decided that those women whose results had come back as negative would have a repeat test.
Dr McKenna said: "The women in whom the test altered, were informed by CervicalCheck in February.
"There was a small number of the 800 women in whom the results were different and they were informed directly by CervicalCheck ... so the women who were affected were informed as soon as it was known."
He said the computer system of the US laboratory involved was designed to communicate with the computer system in Ireland and that triggers a "cascade of letters".
Dr McKenna said: "It was appreciated that that wasn't working and a manual system was put in place as far as the HSE knew."
When asked to clarify who knew about the computer glitch, he said it was "appreciated within the screening service".
Dr McKenna said: "The HSE were reassured by the fact that ... their (the women's) GPs were being written to manually."
Asked when it became known that this had not happened, he said it "only came to the knowledge of the screening programme and the HSE in early July".
Dr McKenna said: "The HSE and the screening service are very disappointed that the arrangement that they thought had been put in place was not working and this will be investigated as to why this element wasn't followed through by the contractor."
Woman told 'some type of IT glitch' led to delay
Meanwhile, the woman whose queries uncovered the computer glitch has said that it took months of repeated calls and emails for her to get to the bottom of the problem.
'Sharon' said she finally got her results over the phone at the end of June - seven months after having her test - and realised there was "a huge potential issue" that women may have results requiring follow up and be none the wiser.
This led her to express her concerns to CervicalCheck and subsequently her opting to have a private smear test.
Speaking on RTÉ's Morning Ireland, 'Sharon' said she had her smear test in early December 2018 with her GP and expected results in writing six weeks later.
When it did not arrive, she started to query her GP in February and was advised it could take up to 14 weeks due to the backlog in the system.
'Sharon' said she just "really wanted was to get the results and know I was okay" and phoned CervicalCheck on a number of occasions, but could not get any results.
In early April, she contacted the Department of Health and was informed that they would look into it.
She said she sent two more emails and on 30 April got an email to say the delay was due to the backlog, which happened after free tests were offered to women last year.
'Sharon' was also told it was "not necessarily dangerous" as there was a low-risk and even if it was cancer it would possibly take 10-15 years to develop.
She had some further correspondence with the Department of Health before a phone call was made on 26 June to her from a senior doctor in CervicalCheck who gave her her results and told her there had been "some type of IT glitch" and that a decision had been made not to inform the affected women.
She later found out her GP had the results since 19 June but had not been made aware that no letter had been sent to her from CervicalCheck.
Minister for Health Simon Harris described the latest issue as one of "great frustration, annoyance and worry" for women.
Speaking in the Seanad this morning, he said he welcomed the apology the HSE has now given to the women affected.
Mr Harris said he does not want women to be worried about a clinical risk that may not exist, despite the fact that what has happened was upsetting from an "administrative point of view".
He added that it was important to say that the overwhelming amount of tests involved were precautionary retests for the HSE and that the original test results were unlikely to change.
The minister said he expected that a backlog in carrying out cervical smear tests to be eliminated by the autumn and that additional lab capacity had been secured.
Mr Harris said that Ireland was now moving towards introducing the HPV test, which he said will reduce the number of false negative and false positives and that the HPV vaccine for boys will be rolled out in schools from September.
"We can now say with honesty, that within a generation we can effectively eradicate cervical cancer in our country," he said.
The Irish Patients' Association has called on Minister Harris to set up an independent review into the issue.
Fianna Fáil's health spokesperson Stephen Donnelly said women need answers and the current scenario sees some women waiting a year or longer for results.
Speaking on RTÉ's Today with Sean O'Rourke, he said that while there are political implications, the main concern was whether there were health implications for any of the women involved.
Labour's health spokesperson Alan Kelly said that it was critical to have confidence in the National Screening Programme.
He told RTÉ's News at One that he was worried that the HSE "could not deal with an issue promptly to ensure that confidence is maintained".
Additional reporting Laura Hogan