Several stroke severity tools help EMS differentiate between a large vessel occlusion (LVO) and other types of stroke, but the most widely referenced in EMS training and clinical guidelines are the RACE scale, FAST-ED, LAMS, VAN, and the Cincinnati Prehospital Stroke Severity Scale (CPSSS or C-STAT). These tools go beyond simply detecting whether a stroke is happening. They help paramedics gauge how severe it is and whether the patient needs to bypass a closer hospital in favor of a comprehensive stroke center equipped to perform clot-retrieval procedures.
Why Severity Tools Matter for EMS
Basic stroke screening tools like the Cincinnati Prehospital Stroke Scale (CPSS) and FAST (Face, Arm, Speech, Time) are designed to answer one question: is this person having a stroke? They’re fast and easy to use, but they don’t tell you much about what kind of stroke it is. A large vessel occlusion, where a major artery feeding the brain is blocked, requires a specialized procedure called endovascular thrombectomy. That procedure is only available at comprehensive stroke centers, not at every hospital with a stroke team.
This is where severity scales come in. They test for signs that point specifically to large vessel involvement: gaze deviation (eyes pulling to one side), neglect (the patient ignoring one side of their body), vision loss, and significant weakness. If a severity tool scores above a certain threshold, EMS protocols typically direct the crew to transport the patient to a comprehensive stroke center, even if a primary stroke center is closer. Current triage guidelines recommend routing suspected LVO patients directly to a comprehensive stroke center when it can be reached within 45 to 60 minutes of transport time.
RACE Scale
The Rapid Arterial Occlusion Evaluation (RACE) scale is one of the most commonly used LVO screening tools in the field. It evaluates five items: facial palsy, arm motor function, leg motor function, gaze deviation, and either speech problems (for patients with right-sided weakness) or body neglect (for patients with left-sided weakness). The total score ranges from 0 to 9, and a score of 5 or higher raises high suspicion for a large vessel occlusion. In meta-analyses, RACE shows moderate sensitivity (around 0.69) with high specificity (0.80), meaning it’s quite good at confirming an LVO when it flags one, though it will miss some cases.
FAST-ED Scale
FAST-ED builds on the familiar FAST framework by adding assessments for eye deviation and the ability to follow simple commands, which test for neglect. A score of 4 or higher suggests LVO. When tested with paramedics assessing patients in the field, FAST-ED achieved 80% sensitivity for detecting large vessel occlusions. Among confirmed ischemic stroke patients specifically, accuracy improved further. Its specificity in meta-analyses sits around 0.80, making it one of the more balanced tools for prehospital use.
LAMS (Los Angeles Motor Scale)
LAMS is a five-point scale focused entirely on motor findings. It checks three things: facial droop (0 or 1 point), arm weakness (0, 1, or 2 points depending on whether the arm drifts slowly or rapidly), and grip strength (0, 1, or 2 points for normal, weak, or absent grip). Scores of 4 or higher are considered suspicious for LVO. LAMS carries the highest specificity of the major prehospital scales at 0.85, meaning it produces relatively few false alarms. The tradeoff is that it doesn’t assess cortical signs like gaze deviation or neglect, so it can miss some LVO presentations that show up primarily as cognitive rather than motor deficits.
VAN (Vision, Aphasia, Neglect)
The VAN scale, introduced in 2016, takes a different approach. Rather than assigning a numeric score across several motor tests, it screens specifically for cortical signs that suggest large vessel involvement: vision changes, language problems (aphasia), and neglect. A VAN score of 1 or higher is considered a positive screen for LVO. It was designed as an add-on assessment, typically used after a basic screen like CPSS confirms stroke is likely. The idea is that motor weakness alone can come from many types of stroke, but the combination of motor symptoms with cortical deficits like neglect or vision loss points more specifically toward a large artery blockage.
C-STAT and CPSSS
The Cincinnati Stroke Triage Assessment Tool (C-STAT) evaluates three items: conjugate gaze deviation (scored 0 to 2), level of consciousness (0 or 1), and arm weakness (0 or 1). Total scores range from 0 to 4, with a score of 2 or higher suggesting LVO and triggering transport to an endovascular-capable center. The Cincinnati Prehospital Stroke Severity Scale (CPSSS), a closely related tool, uses a threshold of 2 or higher as well. The original Cincinnati Prehospital Stroke Scale (CPSS) showed the highest sensitivity of all the major tools at 0.91, meaning it catches most LVO cases, but its lower specificity means it also flags many non-LVO strokes.
PASS (Prehospital Acute Stroke Severity)
The PASS scale was developed specifically to identify patients with emergent large vessel occlusion who are most likely to benefit from clot-retrieval procedures. It uses a threshold score of 2 or higher to flag suspected LVO. In comparative analyses, PASS achieved a specificity of 0.80, placing it among the more reliable tools for confirming large vessel involvement. It’s designed to be straightforward enough for field use while still capturing the severity indicators that matter for triage decisions.
How EMS Systems Choose a Scale
No single tool is perfect. The most sensitive option (CPSS, at 0.91) catches nearly all LVO cases but sends more non-LVO patients to comprehensive stroke centers unnecessarily. The most specific option (LAMS, at 0.85) produces fewer false positives but misses more true LVO cases. Clinical guidelines increasingly recommend combining tools, pairing a highly sensitive screen like CPSS for initial stroke detection with a highly specific tool like LAMS or RACE for severity differentiation.
A 2025 meta-analysis in the journal Neurology found that among EMS personnel specifically, the FPSS, ACT-FAST, and FAST-VAN scales achieved the highest overall diagnostic performance, though FAST-ED, RACE, and NIHSS remain the most widely adopted in clinical guidelines due to their familiarity and extensive validation. The most commonly studied scales in prehospital research were CPSS (appearing in 17% of studies), followed by 3ISS, NIHSS, and RACE.
Which tool your local EMS system uses depends on regional protocols, the distribution of stroke centers in the area, and how much additional training time is available. The core goal is the same across all of them: identify the patients who need the most advanced care and get them there as quickly as possible, because every minute of delayed blood flow to the brain means more permanent damage.