The Supreme Court will give its decision later on an appeal against a High Court judgment in the case of Limerick woman Ruth Morrissey, who is terminally ill with cervical cancer.
A key issue is the High Court's finding that screeners should have "absolute confidence" that a smear test has no abnormalities before passing it as clear.
The five judge court's decision in the case will deal with the legal standard of care for cervical screening and is seen as a test case which could affect other cervical cancer cases and the work of the CervicalCheck tribunal.
After a three-day appeal, the Chief Justice Frank Clarke said it was a "very difficult" case both because of its underlying and tragic conditions and the legal issues with very wide implications.
He said the court would try to give its judgment in a way that "brings clarity" to this area as quickly as possible.
The HSE and two laboratories - Quest Diagnostics Ireland Ltd and Medlab Pathology Ltd - have appealed the July 2019 judgment by the High Court's Mr Justice Kevin Cross awarding €2.1m to Ms Morrissey and her husband Paul over misreading of Ms Morrissey's cervical smear slides.
The Government has guaranteed the award of damages irrespective of the outcome of the appeal.
Lawyers for the HSE and two laboratories say the High Court judgment had far reaching consequences for cancer screening services and medical diagnosis generally as well as for the CervicalCheck tribunal and other litigation relating to cervical cancer.
Lawyers for Ms Morrissey and her husband - who were awarded the €2.1 million in damages by the High Court - said the High Court judgment does not have the consequences argued by the labs and the HSE, and was widely misunderstood. They said no new legal test was laid down by the judgement.
Ms Morrissey was diagnosed with cervical cancer in 2014 and her case concerned smears taken under the CervicalCheck screening programme in 2009 and 2012.
She was not told until May 2018 that a 2014 review showed two smears were reported incorrectly.
Her lawyers told the court today that this case was a "human tragedy" which arose entirely out of the fault of all three defendants.
Senior Counsel Jeremy Maher sad an "abundance of evidence" entitled the High Court to conclude Ms Morrissey's cancer was caused by negligence of the laboratory defendants, he said.
A pre-cancer specialist gave "clear evidence" that pre-cancer was present in 2009 and 2012 and was allowed, through the fault of the laboratories, to develop undetected, he said.
Were it not for that negligence, Ms Morrissey would not be facing death in early 2020 or possibly 2021, he said. She had suffered a recurrence of cancer, surgery is not now possible and her treatment is now "effectively palliative".
Patrick Treacy SC who also represents the Morrisseys urged the court to find that a cytoscreener's practical duty is to have "absolute confidence" that a slide is normal before reporting it as negative.
Absolute confidence is "absolutely essential" in this "fundamental issue of women's health", he said. "We are dealing with people's lives here, there is no room for mediocrity."
Michael Cush SC, replying for Quest, said the law cannot use words which suggest "absolute confidence" and any such legal requirement, particularly for screeners, is "contrary to logic and common sense".
Because a competent screener will know that some women who go on to develop cancer could have been screened as negative, how could any screener say they have "absolutely confidence" in their screening result, he asked.
Patrick Hanratty SC, for the HSE, said the incidence of cervical cancer was increasing here before the Cervical Check programme but has fallen by 7% year on year since.
The High Court judgment can be interpreted as setting a new absolute confidence test concerning cytology screening and other areas of medicine, he said. An absolute confidence test was "unnecessary" and "capable of causing confusion".
Conor Halpin SC, in reply for Medlab, said it is an Irish company incorporated here and employing screeners who got their qualifications here and it "does not matter that it is part of a US multinational".
Evidence that there were 35,000 cells on the 2012 slide tested by Medlab had not been challenged and the High Court erred in saying Medlab should have found that slide was inadequate for screening, he argued.
Vicky Phelan was among a number of CervicalCheck campaigners who attended the final day of the appeal.