Previously it was claimed patients were being discharged too soon
The number of A&E patients admitted to hospital rises dramatically in the last ten minutes of the waiting target, statistics for England show.
The NHS Information Centre finds two thirds of patients still waiting in the last minutes of the four hour target are admitted, compared to 21% overall.
The College of Emergency Medicine says meeting targets may be a factor, but other issues are also at play.
The majority of A&E patients were seen within three hours, figures show.
And 96% of patients were seen and assessed within four.
The four hour target was introduced at the end of 2004 to end long waits at A&E. There have previously been claims that patients were being discharged too early without being properly assessed in order to meet the deadline.
In fact what these figures show is that the longer the patient waited, the less likely they were to be discharged with no follow-up.
Overall 6% of all people are dealt with in these final 10 minutes, but the picture varies from hospital to hospital.
In some departments there is no-one left to be seen in these last few minutes, but in others 15% are still waiting.
On average 66% of those still waiting in the last ten minutes end up being admitted to hospital, compared to 21% overall.
Don McKechnie of the College of Emergency Medicine said the types of patient being admitted needed to be analysed more carefully before any conclusions could be drawn.
"It may take time time to sort those with slightly more complex conditions out, and so decisions about what to do with these patients may not be taken until the later stages. That could be part of it.
"We do not want to admit patients to hospital who do not need to be there - it puts pressure on bed and is simply not fair on the patient concerned. But it seems sometimes that we are damned if we do and damned if we don't."
The head of the NHS Information Centre, Tim Straughan, said hospitals could use the data to learn from each other.
"This report gives a valuable, minute by minute insight into patients' experience of A&E services and highlights a marked variation in both the speed of care and the destination of patients when they leave A&E.
"With data at individual trust level, A&E departments may want to compare how their approach varies with others as there are marked differences from place to place."
Health Minister Mike O'Brien said: "This data shows that the overwhelming majority of A&E patients were seen within three hours, well within the four-hour standard. This shows continued dedication and hard work on part of NHS staff across the country.
He added: "Meeting the standard does not mean that the quality of care is compromised. We have always made it clear that quality of care and clinical need must come first and we expect trusts to ensure that patient safety is their first priority."
Unison's head of health, Karen Jennings, said: "It is good news that the overwhelming majority of patients are seen within three hours.
"But this information will help the small number of A&E services that appear to be admitting patients to avoid exceeding targets.
"Overall, outcomes for patients are good, but we always need to look at ways we can improve patient care for all."