The health board are buckling under the pressure brought about by the winter weather with outbreaks of flu, respiratory illness and people falling in icy conditions, adding to their already considerable woes. In the latest weekly figures, just 77.3% of patients were dealt with within the four-hour target.
At the Royal Infirmary of Edinburgh, more than a third of patients had to wait longer than four hours.
The flagship hospital was the worst performing of all Scottish emergency departments with just 64.1 per cent of patients being seen within the four-hour target.
More than half of patients (54 out of 107) in Scotland waiting for over 12 hours in A&E were in NHS Lothian.
This comes on the back of an internal audit into NHS Lothian drawing up local guidelines on how waiting times should be recorded because staff found the national guidance was “vague and ambiguous”.
As a result patients waiting longer than the four hour Scottish Government target was under-reported in all of NHS Lothian’s emergency departments - at the Royal Infirmary, the Western General, the Royal Hospital for Sick Children and St John’s Hospital, Livingston.
Before the misreporting came to light in October the health board had been meeting the government's target of 95%.
Health Secretary Shona Robison said: “We are specifically working with NHS Lothian to help identify and provide solutions to improve flow through the hospital, which in turn will boost its performance and improve waiting times for patients.”
NHS Lothian's deputy chief executive, Jim Crombie, said: "Like a number of other health boards, NHS Lothian is experiencing significant winter pressures across our whole healthcare system.
"There are a number of contributing factors, including the increasing complexity of cases presenting at emergency departments and significant numbers of delayed discharges.
"This new way of working will allow us to zoom in on processes and procedures, not just in the emergency department, but across the acute care system to help improve patient flow through our hospitals."