What is the NIHSS score?

The NIH Stroke Scale (NIHSS) is a 15-item (11-domain) clinical assessment tool used to quantify the severity of acute ischemic stroke. Scores range from 0 (no stroke symptoms) to 42 (maximum severity). It evaluates level of consciousness, gaze, visual fields, facial palsy, motor strength in all four extremities, limb ataxia, sensory function, language, dysarthria, and extinction/inattention. The NIHSS is the most widely used stroke severity scale worldwide.

How is the NIHSS scored?

The NIHSS consists of 11 domains with 15 individually scored items. Each item is scored from 0 (normal) to a maximum of 2–4 depending on the domain. Some items allow 'UN' (untestable) for amputations or joint fusions — these score 0 for the total but should be documented. The examiner should score the first response observed and not coach the patient. The total score is the sum of all individual item scores.

What NIHSS score qualifies for tPA treatment?

There is no strict NIHSS cutoff for tPA eligibility. Per AHA/ASA guidelines, IV alteplase is recommended for acute ischemic stroke patients presenting within 4.5 hours of symptom onset. While NIHSS is used to assess severity, both mild (NIHSS 25 is associated with higher risk of hemorrhagic transformation. The decision to treat involves clinical judgment weighing benefits and risks for each patient.

What do different NIHSS scores mean?

NIHSS scores are classified as: 0 = no stroke symptoms, 1–4 = minor stroke, 5–15 = moderate stroke, 16–20 = moderate-to-severe stroke, and 21–42 = severe stroke. Higher scores correlate with larger infarct volumes, worse functional outcomes, and higher mortality. Serial NIHSS measurements can track improvement or deterioration — a change of ≥4 points is generally considered clinically significant.

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NIH Stroke Scale (NIHSS) Calculator

Quantify stroke severity using the 11-domain NIH Stroke Scale. Score range: 0–42.

Inputs

1a. Level of Consciousness

1b. LOC Questions (month, age)

1c. LOC Commands (open/close eyes, grip/release hand)

2. Best Gaze (horizontal eye movements)

3. Visual Fields

4. Facial Palsy

5a. Motor Arm — Left (hold at 90°/45° for 10 sec)

5b. Motor Arm — Right

6a. Motor Leg — Left (hold at 30° for 5 sec)

6b. Motor Leg — Right

7. Limb Ataxia

8. Sensory

9. Best Language

10. Dysarthria

11. Extinction / Inattention

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Complete all items to calculate NIHSS score.

0No stroke symptoms

1–4Minor stroke

5–15Moderate stroke

16–20Moderate-severe stroke

21–42Severe stroke

Disclaimer: For educational purposes only. Not a substitute for clinical judgment.

When to use

The NIHSS is used to quantify stroke severity at presentation, guide treatment decisions (including thrombolysis and thrombectomy), and monitor neurological status serially. It is a required component of acute stroke care protocols.

Clinical pearls

There is no absolute NIHSS cutoff for tPA — clinical judgment guides eligibility within the treatment window.
NIHSS > 25 is associated with high mortality and increased risk of hemorrhagic transformation with thrombolysis.
Serial NIHSS assessments (e.g., q1h for 24h post-tPA) are critical for detecting improvement or deterioration.
NIHSS may underestimate posterior circulation strokes (brainstem, cerebellar) which can be devastating despite low scores.

References

Brott T, et al. Measurements of acute cerebral infarction: a clinical examination scale. Stroke. 1989;20(7):864-870.
NINDS rt-PA Stroke Study Group. Tissue plasminogen activator for acute ischemic stroke. N Engl J Med. 1995;333(24):1581-1587.

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About This Tool

What Is the NIH Stroke Scale?

The National Institutes of Health Stroke Scale (NIHSS) is a standardized clinical assessment tool developed by Thomas Brott and colleagues in 1989 to quantify the severity of neurological deficits caused by acute ischemic stroke. It evaluates 11 domains across 15 items, producing a total score from 0 (no deficit) to 42 (maximum severity). The NIHSS has become the standard for stroke severity assessment worldwide and is used in emergency departments, stroke units, and clinical trials to guide treatment decisions and track patient progress.

How to Perform the NIHSS

The NIHSS should be performed in the order listed, scoring each item based on the first response observed — do not coach or repeat instructions. Each item is scored on an ordinal scale, with 0 representing normal function. The motor arm and leg items are tested individually for left and right sides. Items that cannot be tested due to pre-existing conditions (e.g., amputation, joint fusion) are scored as "UN" (untestable) and count as 0 toward the total. The entire assessment typically takes 5–8 minutes to complete.

Clinical Significance

The NIHSS score correlates with infarct volume, functional outcome, and mortality. Scores of 1–4 indicate minor stroke with generally good prognosis, while scores >20 suggest severe stroke with high mortality risk. The NIHSS is used to guide decisions about intravenous thrombolysis (alteplase), mechanical thrombectomy, and level of care. Serial NIHSS measurements help detect clinical deterioration (e.g., stroke progression, hemorrhagic transformation) and measure treatment response.

🔑 Clinical Pearls

The NIHSS is weighted toward anterior circulation deficits — it may underestimate posterior circulation (vertebrobasilar) strokes, which can be catastrophic despite low scores.
A change of ≥4 points on serial NIHSS is generally considered clinically significant and should prompt reassessment.
For tPA eligibility, there is no strict NIHSS cutoff, but scores >25 carry increased hemorrhagic risk. "Mild but disabling" symptoms (low NIHSS) may still warrant treatment.
NIHSS certification requires formal training — ensure examiners are certified for accurate, reproducible scoring.

Key References

Brott T, et al. Measurements of acute cerebral infarction: a clinical examination scale. Stroke. 1989;20(7):864-870.
NINDS rt-PA Stroke Study Group. Tissue plasminogen activator for acute ischemic stroke. N Engl J Med. 1995;333(24):1581-1587.
Powers WJ, et al. Guidelines for the Early Management of Patients With Acute Ischemic Stroke: 2019 Update. Stroke. 2019;50(12):e344-e418.

Formula last verified: February 2026