Ambulance crews in Cambridgeshire are piloting the use of finger-prick blood tests to diagnose the deadliest form of stroke, with preliminary data suggesting they may be up to twice as effective as relying on patients’ symptoms alone.
The tests, which work on a similar principle to the lateral flow tests (LFTs) used to detect Covid, are designed to rapidly identify whether someone suspected of having a stroke has suffered a large vessel occlusion (LVO), where a blood clot blocks a major artery in the brain.
Although LVOs account for about a third of strokes, they are responsible for 95% of disabilities and deaths. However, a patient’s chances of recovery are markedly improved if they undergo a thrombectomy procedure to manually remove the clot within hours of symptom onset.
The problem is that there are only 24 hospitals in the UK that can provide thrombectomy treatment, and LVO is difficult to diagnose without a brain scan because many other conditions show similar symptoms.
Unless a patient is lucky enough to live near a specialist centre, they will usually be assessed at a general hospital and then transferred. According to national audit data from 2022-23, it takes an average of three hours or more from arriving at a first hospital to arriving at a thrombectomy centre.
“Early identification of LVO strokes by ambulance clinicians could offer opportunities for fast-tracking patients to thrombectomy-capable hospitals, avoiding delays to care when taken to other non-specialist hospitals,” said Larissa Prothero, an advanced research paramedic at the East of England ambulance service NHS trust (EEAST), which is involved in the feasibility study.
The test, which consists of two lateral flow cartridges, was developed by the Cambridge-based firm UpFront Diagnostics, and is designed to detect two molecules in the blood: The first is a clot-related protein called D-dimer. The second, called GFAP, is associated with bleeding in the brain; its absence helps to rule out a haemorrhagic stroke, where a blood vessel ruptures and bleeds.
Earlier studies suggest that the kit can detect LVO within 15 minutes, with about 90% accuracy. This is “more than double that of current methods used in the ambulance, which involve checking [symptoms]”, said Gonzalo Ladreda, UpFront’s chief executive officer.
Dr Louise Flanagan, the head of research for the Stroke Association, which helps to fund the early development of the LVOne test, said: “When it comes to diagnosing a stroke, there’s a window of about four to six hours to deliver a thrombectomy or a thrombolysis [where drugs are used to dissolve the clot], but the faster the better.
“Having a rapid test that can be administered by the ambulance crew would mean that that person can get the right treatment for them quicker, which is going to save brain cells and hopefully limit the disability afterwards.”
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EEAST is rolling out the tests to paramedics in south Cambridgeshire to assess the feasibility and safety of integrating them into real-life clinical settings. The data will be submitted to regulators to help assess their suitability for use within the UK.
The Stroke Association is also sponsoring a separate trial of a saliva-based stroke test, which recently launched in the West Midlands.
As well as saving lives, such tests also have the potential to save the NHS money, said Flanagan. “There could be direct cost savings in terms of ambulance journeys and imaging. If that person is leaving hospital with fewer disabilities and fewer side-effects from that stroke, there are also going to be long-term savings in terms of rehabilitation and social care.”
