The doctor who mistook an X-ray of an ankle for an elbow left the Midlands Regional Hospital Portlaoise with a negative reference highlighting concerns about his abilities but his subsequent employers never saw it.

Dr Omar Hassan (30) received the reference from a hospital consultant when he left the Midlands Regional, having been suspended from clinical practice.

The Sudanese doctor went on to work at public hospitals in Mayo and in Galway, where colleagues became so concerned about his performance that he was suspended and later reported to the Medical Council.

However, the Sunday Independent has learned that Dr Hassan left the Portlaoise hospital with a negative reference that it is understood was not shown to his employers at Mayo General Hospital or Galway University Hospital apparently on the strength of two positive references from doctors in his native Sudan.

Dr Hassan was found guilty last week of 28 counts of poor professional performance and professional misconduct after moving freely from one hospital to the next.

The Medical Council hearing heard a catalogue of examples of Dr Hassan's alleged poor performance. His colleagues at Galway University Hospital were so concerned about Dr Hassan's ability that they checked the medical registrar to see whether he was actually registered.

One patient told how she became upset when Dr Hassan repeatedly tried to insert a needle into her arm but was not able to find a vein, even after she became distressed and asked him to stop.

The case has raised concerns over how doctors are checked as they move from hospital to hospital. One of the key issues to emerge from it is whether and to what extent Dr Hassan's medical references were checked.

Minister for Health Leo Varadkar has requested a review of recruitment and checking procedures. The Irish Independent reported that even after he was placed on administrative leave by Galway University Hospital, Dr Hassan went on to secure work through a locum agency and was even offered a full-time post at Our Lady's Hospital in Navan in early 2015.

The Dublin Midlands Hospital Group and the Saolta group, which covers Galway and Mayo, said Dr Omar Hassan was recruited through standard HSE procedures.

The Dublin Midlands Hospital Group said Dr Hassan was interviewed for the post of surgical senior house officer on July 4, 2012. He had positive references from two consultant surgeons in Sudan.

He began work as a junior hospital doctor on July 17, 2012, but within a week was taken off night call because of concerns noted by staff. "Following further supervision and training he was subsequently suspended from any clinical work in the autumn of the same year," it said.

It confirmed that one consultant from the hospital supplied a reference "reflecting the performance of Dr Hassan during his period at MRHP".

Dr Omar Hassan Khalafalla Mohamed was registered with the Medical Council in July 2012. He is from Sudan and graduated from the University of Khartoum in 2008.

Dr Hassan went on Liveline after the Medical Council verdict to defend himself, claiming he had not harmed patients. He said his father was a surgeon in Sudan and had worked in Jervis St Hospital in the 1970s. "I have been treated unfairly and very badly with unfair allegations," he said. The Medical Council has yet to decide on sanctions against Dr Hassan.

Sunday Independent