A national medical exam is needed, say experts, after a study showed there was a variation in graduate performance.
The study looked at over 5,800 graduates
Universities are free to set the tests and courses medical students do in their five-year degrees.
The study of 5,800 graduates found ones from Oxford, Cambridge and Newcastle performed better in postgraduate tests, the BMC Medicine journal reported.
Professor Chris McManus, of University College London, said a national system would allow comparisons to be made.
Medical courses and the way students are assessed varies from medical school to medical school.
All they have to do is ensure standards set by the General Medical Council are met.
Professor McManus said: "Not all medical schools are equal. We assume, because there are national standards, that all graduates have the necessary skills, but there is no way of comparing performance.
"If we had a national examination like they do in the US we could be assured about standards.
"It would also allow hospitals, when they are picking junior doctors, to know which ones had performed better at university. This is important if we are going to have a competitive market as seems to be developing."
The team, led by Professor McManus, looked at the performance of medical graduates who took the postgraduate MRCP test set by the UK royal colleges of physicians.
The exam is traditionally taken 18 months after graduation and is aimed at doctors who want to become radiologists, oncologists and consultant physicians.
In total, about a third of medical graduates end up taking the three-part exam.
Researchers found there were differences in the graduates who passed it at their first attempt.
Some 91% of doctors who studied at Oxford University passed the initial part first time, compared to 76% from Cambridge, and 67% from Newcastle.
This compared to 32% from Liverpool and 38% from Dundee.
Professor McManus said: "You would expect Oxford and Cambridge graduates to perform better, but there is a two-fold difference between Liverpool and Newcastle.
"Most of this has to be because of the different quality of graduates."
A General Medical Council spokeswoman said a review of medical education was being prepared with a national examination a possible option.
She added: "We recognise the need to ensure that medical education meets the needs of a changing society."
But the British Medical Association said it opposed such an exam.
John Hallett, of the BMA's students committee, said: "A national exam would mean that rather than teaching medical students how to be doctors, medical schools would end up focussing on teaching students how to pass exams."