GPs and other health professionals should be more proactive in offering at-risk groups HIV tests, experts say.
Many people are unaware they are infected with HIV
The University College London study of 263 HIV-positive African patients in the UK found half were diagnosed late despite above average use of services.
And in 80% of these cases, the issue of HIV testing had not been discussed with a doctor, the Aids journal said.
Campaigners said doctors were often put off such a subject because of fear of offending patients.
There are estimated to be over 63,000 adults living with HIV in the UK, two thirds of whom have been infected via heterosexual sex.
The majority of these are people who caught the infection abroad and of African origin.
The study said the introduction of highly-active antiretroviral therapy means that if HIV is diagnosed early - before symptoms show - then in most cases it becomes a chronic condition rather than terminal illness.
But HIV-positive individuals who are diagnosed later are approximately 14 times more likely to die within one year of diagnosis than those identified early.
Lead researcher Dr Fiona Burns believes GPs in particular should be more proactive.
"What we are seeing here is a failing to utilise opportunities for earlier diagnosis of HIV.
"People are dying because they are not being tested early enough.
"We need to be in a position where GPs are prepared to discuss HIV risks and offer tests as a matter of course to people from at-risk communities."
The findings of the research, funded by the Wellcome Trust, come after recent advice from England's chief medical officer, Sir Liam Donaldson.
He said health professionals should "be alert to the circumstances in which it is appropriate to offer and recommend an HIV test".
Lisa Power, of the Terrence Higgins Trust, said: "I think doctors are worried about suggesting it because they feel it may offend their patient because of the stigma.
"But I think GPs should be encouraged to broach this subject and patients should be made aware that it is fine to be asked."
Dr Ewen Stewart, of the Royal College of GPs, said it was an "extremely important issue".
"GPs have an important role in increasing levels of HIV testing in the population.
"In order to do this we need to be proactive about raising the issue of HIV testing with people who may have been at risk and then carrying out the HIV testing in general practice settings."