NIHSS Score Ranges for Stroke Severity Classification
The NIHSS score ranges that define stroke severity are: mild stroke 0-5, moderate stroke 6-14, and severe stroke ≥15.
Standardized Classification
The most recent and authoritative guideline consensus establishes clear NIHSS thresholds for categorizing acute stroke severity 1:
- Mild stroke: NIHSS 0-5
- Moderate stroke: NIHSS 6-14
- Severe stroke: NIHSS ≥15
This classification system appears in the 2021 Valve Academic Research Consortium 3 (VARC-3) guidelines, which harmonized definitions across cardiovascular and neurological research 1.
Alternative Classification Systems
Some sources use slightly different categorization schemes, though these are less commonly applied in contemporary practice:
- One classification defines scores <5 as "small stroke" and >20 as "large stroke" 1
- Research studies have occasionally used five-tier systems: ≤5 (minor), 6-10 (mild), 11-15 (moderate), 16-20 (severe), >20 (very severe) 2
Prognostic Implications
The NIHSS score is the strongest predictor of stroke outcomes and directly influences treatment decisions 1:
- NIHSS <10: Approximately 60-70% of patients achieve favorable outcomes at 1 year 1
- NIHSS >20: Only 4-16% achieve favorable outcomes at 1 year 1
- NIHSS >16: Forecasts high probability of death or severe disability 1
- NIHSS <6: Forecasts good recovery 1
Clinical Application Considerations
The NIHSS should be assessed at presentation/admission within the first 24 hours 1. The scale ranges from 0 to 42 points across 15 items evaluating consciousness, vision, motor function, sensation, language, and attention 1.
Important caveat: Patients with NIHSS ≥20 have a 17% risk of intracranial hemorrhage with thrombolytic therapy, which must be weighed against potential benefits 1. Time-to-treatment windows may also vary by severity—moderate strokes (NIHSS 6-14) show benefit from treatment within 120 minutes, while time-to-treatment appears less predictive for mild and severe strokes 3.
All healthcare professionals involved in stroke care should be trained and certified in NIHSS administration to ensure reliable severity assessment and appropriate treatment decisions 1.