The triage system relies on computer software (Advanced Medical Priority Dispatch Software, or AMPDS) to code the level of emergency from the verbal description of symptoms provided by the caller to prioritise the ambulance response.
AMPDS contains several stroke related questions, and people who are unconscious are automatically graded as Category A, which merits an 8 minute ambulance response. Stroke patients who are still conscious warrant a 19 minute response (Category B).
There are around 110,000 cases of stroke each year in the UK. Stroke is the third most common cause of death and the leading cause of severe disability.
An ambulance is called to around half of people who have had a stroke, and the evidence shows that prompt treatment can significantly reduce the risk of major disability and death.
The authors compared the software based clinical coding with the clinical diagnosis made by a doctor for all patients admitted by ambulance from one regional service to the emergency department of one major hospital in southern England.
During the six month study period, almost 5000 patients were admitted by ambulance, 126 of whom were subsequently diagnosed by a doctor as having had a stroke.
But use of AMPDS only picked up 60 patients who had had a stroke; the remaining 66 were given another diagnosis. Fewer than one in four stroke patients were given a Category A ambulance response, and 3% were given a Category C response (60 minute response).
The system also coded 62 other patients as having had a stroke, when they had other problems.
AMPDS was developed to help call takers, most of whom have no medical training, and only up to 21 hours of dispatcher training, to prioritise symptoms accurately.
Since 2002, all UK ambulance services have used some decision based tool, and most use AMPDS. This system is also widely used throughout the rest of Europe and America.
"This first link in the chain of survival needs strengthening in order provide prompt and timely emergency care for these patients," conclude the authors, calling for the Category B response for conscious stroke patients to be upgraded to Category A.