What is the PRE score?

The Pittsburgh Response to Endovascular therapy (PRE) score is a bedside prognostic index for adults with anterior circulation large vessel occlusion (LVO) stroke who are being considered for endovascular therapy (mechanical thrombectomy). It combines three variables available before the procedure: age, baseline NIH Stroke Scale (NIHSS), and ASPECTS on initial non-contrast CT.

PRE was developed to answer a specific question: among patients in whom successful revascularization (TICI grade 2b or 3) can be achieved, who is most likely to gain functional benefit from endovascular treatment versus who may do well anyway or may not improve despite recanalization? It is a patient-selection and counseling tool, not a substitute for emergent stroke protocols, imaging confirmation of LVO, or multidisciplinary judgment.

Clinical context: LVO stroke and endovascular therapy

Acute ischemic stroke from proximal anterior circulation occlusion (internal carotid artery terminus, M1, or M2 segments) often causes large deficits and extensive penumbra. Randomized trials established that endovascular thrombectomy improves outcomes in selected patients within appropriate time windows when performed at experienced centers.

Not every patient with LVO derives the same incremental benefit from recanalization. Older age, higher NIHSS, and lower ASPECTS (more early ischemic change on CT) correlate with worse baseline prognosis and larger final infarcts. PRE integrates these factors into a single continuous score that maps to strata described in derivation and multicenter validation cohorts (Grady Memorial Hospital, UPMC, Vall d'Hebron).

This calculator applies to patients ≥18 years with anterior circulation LVO, typically presenting within 8 hours of symptom onset, when ICA-T, M1, or M2 occlusion is confirmed and endovascular therapy is clinically contemplated. Posterior circulation strokes and patients outside the studied populations require caution when extrapolating PRE estimates.

The three input variables

Age (years)

Enter chronological age in whole years. Age enters the formula linearly: each additional year increases PRE by 1 point. Advanced age is associated with lower rates of independent outcome after large strokes even when reperfusion is successful, reflecting comorbidity, reserve, and hemorrhagic risk.

NIHSS (National Institutes of Health Stroke Scale)

Enter the baseline NIHSS total at presentation (integer 0–42). NIHSS quantifies neurologic deficit severity across consciousness, gaze, visual fields, motor, ataxia, sensory, language, and neglect domains. In PRE, NIHSS is weighted by a factor of 2, so a 1-point increase in NIHSS adds 2 points to the score. Higher NIHSS strongly shifts patients toward higher PRE strata.

If you need item-level NIHSS scoring, use a dedicated NIHSS calculator and transfer the total into PRE. Use a consistent time point (for example first reliable exam in the ED) documented in the chart.

ASPECTS (Alberta Stroke Program Early CT Score)

Enter ASPECTS on the admission non-contrast head CT (integer 0–10, where 10 indicates no early ischemic change in the ASPECTS territories). ASPECTS summarizes extent of early hypoattenuation in basal ganglia and MCA cortex regions. In PRE, ASPECTS is multiplied by 10 and subtracted from the score, so lower ASPECTS (more established infarct) increases PRE substantially. A drop from ASPECTS 10 to 8 removes 20 points from the net formula through the subtraction term.

Formula and worked structure

PRE Score = age (years) + 2 × NIHSS − 10 × ASPECTS

Example: age 72, NIHSS 18, ASPECTS 7:

• Age contribution: 72
• NIHSS contribution: 2 × 18 = 36
• ASPECTS contribution: −10 × 7 = −70
• PRE = 72 + 36 − 70 = 38

The score can be negative when ASPECTS is high and NIHSS is relatively low. Negative values are expected and meaningful within the published strata.

Endovascular benefit categories

The calculator assigns one of three benefit categories used in this implementation:

PRE score	Category	Interpretation
< −24	Unlikely to need endovascular benefit ("too good" stratum)	Patients often have favorable baseline characteristics. Derivation cohorts suggested limited incremental benefit from successful recanalization compared with lower PRE scores, because many may do well regardless. Consider whether endovascular therapy is necessary; individual factors remain paramount.
−24 to +49	Likely to benefit if reperfused	Patients in this range are likely to derive maximum benefit from endovascular reperfusion when TICI 2b/3 is achieved. Favorable PRE stratum for considering thrombectomy when clinically appropriate and revascularization is achievable.
≥ 50	Least likely to benefit	Patients are least likely to benefit from endovascular therapy. In validation work, rate of good outcome (mRS 0–2) or final infarct size was not meaningfully affected by TICI 2b/3 reperfusion in this group. Therapy may be futile for preventing disability; use as adjunct to judgment, not a replacement.

Prognostic quartiles (derivation paper)

In addition to benefit categories, the original publication described quartile-style groupings for prognosis:

• PRE < 0
• PRE 0–24
• PRE 25–49
• PRE ≥ 50

These bands refine risk communication within the broad "likely benefit" window and highlight progressively worse expected response to reperfusion at higher scores. Document both the numeric PRE and the category when discussing cases with neurology and neurointerventional teams.

Relationship to TICI reperfusion grades

PRE assumes the clinical question is framed around successful endovascular revascularization, typically defined as modified TICI 2b or 3 (adequate reperfusion of the downstream territory). The score does not predict procedural success; it estimates expected functional and infarct outcomes if that level of reperfusion is achieved.

Patients with high PRE who do not achieve TICI 2b/3 may have poor outcomes for both procedural and biologic reasons. Conversely, low PRE patients who fail recanalization may still deteriorate. Always separate selection for attempt from intraprocedural result.

How PRE differs from other stroke scores

NIHSS alone captures deficit severity but not age or early CT infarct extent. ASPECTS alone captures imaging but not clinical deficit or age. Generic ICU scores are not calibrated to LVO thrombectomy benefit conditional on reperfusion.

PRE is purpose-built for neurointerventional triage in anterior LVO and is simpler than some multivariable models requiring additional labs or perfusion parameters. Modern practice increasingly uses advanced imaging (CT perfusion, MRI) and extended time windows; PRE remains anchored to the classic admission CT + NIHSS + age paradigm from its validation era. Integrate contemporary guideline eligibility (time, imaging, comorbidity) before deferring therapy based on PRE alone.

Practical use in the angio suite pathway

• Pre-procedure huddle: compute PRE after NIHSS and ASPECTS are available to frame expected benefit if TICI 2b/3 is achieved.
• Family discussion: translate strata into plain language about chances of independence and infarct burden, without implying PRE denies standard-of-care therapy.
• Quality and research: risk-adjust comparisons of outcomes by PRE band across centers when definitions are standardized.
• Reassessment: PRE uses baseline variables; it does not update dynamically with post-treatment imaging unless you deliberately recalculate for scenario modeling.

Limitations and cautions

• Derived in specific anterior LVO populations within roughly 8 hours; extrapolation to late-window perfusion-selected patients requires caution.
• Does not incorporate posterior circulation occlusion, distal medium vessel occlusions outside the original scope, or tandem carotid lesions unless your team applies expert judgment.
• Does not replace institutional protocols for IV thrombolysis, blood pressure management, or anesthetic approach during thrombectomy.
• High PRE does not automatically contraindicate thrombectomy when guidelines and patient values support intervention; it signals diminished expected benefit conditional on reperfusion.
• Low PRE does not eliminate hemorrhagic transformation risk or need for ICU monitoring.

Always document the numeric inputs, calculated PRE, benefit category, and whether management followed PRE messaging or deviated for clinically documented reasons.

Using this CalcMD calculator

Enter age (18–120 years), NIHSS (0–42, integer), and ASPECTS (0–10, integer). The tool computes PRE, shows the age, NIHSS, and ASPECTS contributions, assigns the endovascular benefit category (−24 to +49 favorable window, < −24 and ≥ 50 extreme strata), and displays the prognostic quartile label. Use output for education and structured documentation alongside emergent stroke pathways, not as the sole determinant of care.