The Liverpool Care Pathway for the Dying Patient is recommended nationally but media reports in recent months have criticised it as 'the equivalent of euthanasia for the elderly'.
Durham University researchers found just 47.4% of dying patients had been placed on the pathway over the past two decades.
They said this may be due to clinicians' lack of awareness of the programme, staff turnover and concerns about suitability for those with complex conditions.
The Liverpool Care Pathway, developed by the Marie Curie Hospice Liverpool and the Royal Liverpool University Hospitals in 2003, provides healthcare staff with a standardised approach to co-ordinate care for patients' last 72 hours of life. It is now in use in primary and secondary care both in the UK and overseas.
NICE rates the pathway as good practice, and the DH had actively encouraged PCTs to adopt the pathway in the past. Nevertheless, the pathway has attracted critical media attention in recent years.
Although a 2011 audit suggested 90% of hospital wards in England used the Liverpool care pathway, patient uptake remains unclear.
In the study, researchers collected data from 17 clinical studies between 1990 and 2012. They found that 18,052 patients in these studies were placed on the Liverpool Care Pathway - under half of all dying patients.
Just one study examined the proportion of all dying patients eligible for the pathway. Nevertheless, this found a significant minority - around a third - had been left off the pathway.
Researchers concluded: 'The Liverpool Care Pathway is a well-known and well-regarded palliative care tool and this study confirms that it is used in a variety of geographical and clinical settings.
'However, this study provides evidence that around half of all dying patients were not placed on the LCP despite its availability. This raises questions about clinicians’ levels of knowledge and awareness about the LCP, and the appropriateness and applicability of this pathway.'
They said it was possible clinicians were 'unconfident or unaware' of the pathway, or deemed it inappropriate for certain patients.
Authors said there needed to be a more open discussion about the Liverpool Care Pathway and how it is used.