An expert on cervical screening has told the High Court that some cells on a cervical smear taken from Limerick woman Ruth Morrissey in 2009 clearly showed signs of abnormality.

Dr Michael McKenna, a consultant cytopathologist in charge of one of the north's four laboratories responsible for cervical screening, is giving evidence in Ms Morrissey's case against the HSE and two US laboratories - Quest Diagnostics and Med Lab Pathology - over the alleged misreading of cervical smears and the failure to tell her about it sooner.

Ms Morrissey was diagnosed with cervical cancer in 2014 and with a recurrence of the disease a year ago. 

She was informed in May last year that a review in 2014 and 2015 of smears taken under the Cervical Check screening programme had found two smears in 2009 and 2012 were reported incorrectly. 

She claims if she had known this, she would have asked for more scans and better surveillance of her condition.

The court heard that scans this month have been disappointing, and Ms Morrissey's prognosis "remains guarded" despite extensive chemotherapy and radiotherapy treatment.

Dr McKenna examined a slide of the 2009 smear test in October last year. 

This slide was originally screened by Quest Diagnostics, in Grand Rapids, Wyoming in the United States.

He told the court that even at a low magnification, he could see several groups of cells which were darker than others.

This dark staining, called hyperchromatism, was a sign that every one of these groups needed to be looked at in greater detail and he said even at this low magnification he would already have had a heightened level of awareness about the slide.

He said that when he looked at the slide under high-powered magnification, cells in one marked area were up to 99% atypical and some of the cells were clearly abnormal.

Dr McKenna said there was an issue about the adequacy of a slide relating to a smear test carried out on Ms Morrissey in 2012 and screened by MedLab Pathology. 

He said the cell deposit on the slide was "scanty", and he said that examining it, he would have come to the conclusion that there were "well less" than the required amount of 5,000 cells present on it.

He said he did not know of any evidence that MedLab, or anyone else, had carried out any kind of review to justify deviating from the requirement of a 5,000 cell threshold.

Earlier Dr McKenna, who is based at Altnagelvin hospital in Derry, said a slide should never be described as negative for abnormalities if there is any doubt at all in the mind of the screener.

He said cervical screening was a test to check the health of the cells of the cervix. 

He said if any abnormality was detected, a woman could be treated or monitored. 

Dr McKenna said the majority of samples within a screening programme are negative and normal.

However he said the primary screener should have a high sensitivity for detecting abnormalities.

He said there was no "acceptable level" of doubt for a screener to have. If the screener had any doubt about a slide they should pass it on to another screener or a pathologist and should only report a slide as being negative, if they were absolutely certain that it was.

The case is expected to last up to six weeks and is due to continue tomorrow.