NHS Lothian posted statistics that were incorrect with data omitted that had to subsequently be revised by the Information Services Division.
This resulted in an average increase of 1,123 delayed bed days over the period September 2017 to January 2018.
The latest error comes as the troubled health board lurches from one crisis to another with the number of occupied bed days for NHS Lothian far outstripping any other authority.
The total number of delayed days for a single patient is the number of days from when they were medically ready to be transferred to the date they were transferred or discharged
NHS Lothian posted the worst performance for A&E waiting time targets since the publication of weekly figures began three years ago in December 2017.
The health board were forced to remodel reporting practices surrounding emergency department waiting times in December after The Royal Infirmary of Edinburgh, the Royal Hospital for Sick Children and a unit at the Western General Hospital all breached guidelines and under-reported waiting times. Incidents rose from 5.7 per cent in October 2015 to 10.5 per cent in September 2017.
The latest error was flagged up by NHS Lothian after they realised mistakes had been made as computer software crossed over from one system to another.
Shadow health secretary Miles Briggs said: “These updated figures, due to a computer system error, show that delayed discharge figures are even worse in NHS Lothian for September 2017 to January 2018 than we thought.
“Delayed discharge is an ongoing issue and these figures reflect the Social and Health Care crisis affecting NHS Lothian.
“It is deeply concerning that NHS Lothian remains by the far the lowest performing region in Scotland on delayed discharge.
“Delayed discharge can have a huge impact on patients who are stuck in hospital and not able to get back on with their lives.”
“If Nicola Sturgeon thinks that the crisis we have in our NHS over delayed discharge is improving it shows just how out of touch she is and it is definitely not the case in Lothian.
“This is an ongoing crisis that SNP Ministers have consistently failed to deal with over the last 10 years that they have been in charge of NHS Scotland.”
Delayed discharge also known as ‘bed-blocking’ can occur for a variety of reasons, but are usually due to a lack of appropriate care or services available within the community.
Jim Crombie, Acting Chief Executive, NHS Lothian, said: “We have resolved a data collection issue in the statistics we provide to the Information Statistics Division each month in relation to delayed discharges from hospital. It had recently come to light that a small change in a computer system had introduced a minor error for the affected months of September 2017 to January 2018. This only became apparent with the latest data. NHS Lothian’s analytical services picked up the discrepancies, alerted ISD to the problem immediately and made sure it was resolved.