New figures have revealed more than 1,000 patients "gave up" and left A&E without being assessed last year at the Doncaster and Bassetlaw Teaching Hospital NHS Foundation Trust.
A leading expert has expressed concern that hundreds of thousands of patients across England may be coming to harm as a result of leaving hospital prematurely.
Patients who attend A&E are assigned an outcome based on how their visit ended – for instance, whether they were admitted, referred to a specific clinic, or died.
NHS Digital figures show that 1,255 patients were recorded as having left A&E without being seen by medical staff at the Doncaster and Bassetlaw Teaching Hospital NHS Foundation Trust in the 12 months to May .
They joined 307,700 others across England who also left hospital before being assessed or treated.
A spokesman from Doncaster and Bassetlaw Teaching Hospitals said: "All patients who come to the Trust's Emergency Department check-in upon arrival.
"They are seen by a Registered Nurse or doctor who performs a number of assessments.
"Based on this clinical experience, they are then triaged upon their need - those who are seriously ill are seen immediately, while those with less need, and potentially could have been seen by an alternative service such as a GP, are asked to wait, within view of a nurse, and are usually seen within four hours. This rate has been above 90 per cent for the past number of years at the Trust.
"While we would prefer that everyone remained within the service until they are seen, only 1,255 patients did so out of 170,689 registered attendances, a rate of about 0.73 per cent.
"The team is always looking to improve and has recently developed a new, five-year Emergency Department strategy, as well as routinely hosting Quality Improvement (Qi) events within the service, reviewing patient feedback and national best practice to ensure patients receive the best care and treatment within appropriate time-frames.
The rate for people leaving without being seen has worsened in Doncaster and Bassetlaw Teaching Hospital NHS Foundation Trust.
Last May, it stood at 2.7 per cent, up from 0.9 per cent in 2017.
The average across 2018-19 was 0.7 per cent.
However, the figures exclude patients who have an unknown outcome, because staff did not record it.
Rebecca Joyce, chief operating officer at Doncaster and Bassetlaw Teaching Hospitals, said: "All patients who come to our Emergency Departments are assessed and triaged upon arrival by a nurse or doctor.
"Dependent on their conditions, visitors are streamed to the most appropriate service, with those with the most urgent need sent for treatment immediately.
“To ensure the safety of those waiting, a Registered Nurse has a full view of the waiting area at all times. If patients wish to discharge early, they are asked to consult with a clinician first, who, if it is safe, will advise them to see a GP or similar health service or to return if their illness or injury becomes worse.
“Each year, our Emergency Department sees more and more attendances, with July and August being the busiest on record for the Trust. In order to address this challenge, we have recently reviewed and enhanced the service we provide, ensuring patients receive the best care as quickly as possible. As such our services remains one of the best performing in the country.”
Dr Nick Scriven, president of the Society for Acute Medicine, said it was a "major concern to see so many people essentially giving up and leaving".
He added: "The optimistic version is that these people probably did not need emergency care and, when faced with the reality of a long wait, reconsidered.
"The alternative is that they were in need but potentially could have come to harm by leaving unseen."
The number of people who leave without being seen is one of five quality measures used to monitor the performance of A&E departments each month.
During May, the latest month with available data, 1.9 per cent of patients across England left without being seen.
This was an improvement on the same month two years ago, when it was 3.3 per cent.
Of the 1.7 million people who attended an A&E department in England in May, 13 per cent had an unknown outcome – up from just one per cent in 2017.
Dr Scriven said it was concerning to not know what outcomes so many patients had faced.
An NHS spokesman said the proportion of patients leaving without being seen had improved in recent years, despite an increase in an increase in visits to A&E.
He added: "This improvement comes as more people than ever are making use of the NHS 111 phone and online service, which has prevented more than 12 million unnecessary trips to A&E since 2011, by providing people with fast and free advice on more appropriate and convenient options."