Nih Stroke Scale (Nihss) Calculator

What Is the NIH Stroke Scale (NIHSS)?

The NIH Stroke Scale (NIHSS) is a standardized, quantitative neurological assessment tool developed by the National Institute of Neurological Disorders and Stroke (NINDS) to measure stroke severity in clinical and research settings. Clinicians worldwide rely on this 15-item scale to objectively evaluate neurological impairment, guide treatment decisions — including eligibility for thrombolytic therapy — and monitor patient recovery over time.

The NIHSS Formula

The total NIHSS score is the arithmetic sum of all 15 assessed items:

NIHSS = ∑ item_i (i = 1 to 15)

Each item uses an ordinal scoring scale. The maximum achievable total is 42 points. A score of 0 indicates no detectable neurological deficit.

The 15 Assessment Items and Scoring Ranges

• 1a. Level of Consciousness (LOC): 0 (alert and responsive) to 3 (responds only with reflex or autonomic effects)
• 1b. LOC Questions — Month and Age: 0 (both answers correct) to 2 (both answers wrong or unable to speak)
• 1c. LOC Commands — Eyes and Grip: 0 (both commands performed) to 2 (neither command performed)
• 2. Best Gaze: 0 (normal horizontal movement) to 2 (forced deviation or total gaze paresis)
• 3. Visual Fields: 0 (no visual loss) to 3 (bilateral blindness)
• 4. Facial Palsy: 0 (normal symmetrical movement) to 3 (complete paralysis of one or both sides)
• 5a. Motor Arm — Left: 0 (no drift over 10 seconds) to 4 (no movement against gravity)
• 5b. Motor Arm — Right: 0 (no drift) to 4 (no movement)
• 6a. Motor Leg — Left: 0 (no drift at 30 degrees over 5 seconds) to 4 (no movement)
• 6b. Motor Leg — Right: 0 (no drift) to 4 (no movement)
• 7. Limb Ataxia: 0 (absent ataxia) to 2 (ataxia present in two limbs)
• 8. Sensory: 0 (normal sensation) to 2 (severe or total sensory loss)
• 9. Best Language: 0 (no aphasia) to 3 (mute or global aphasia)
• 10. Dysarthria: 0 (normal articulation) to 2 (unintelligible or unable to speak)
• 11. Extinction and Inattention (Neglect): 0 (no abnormality) to 2 (profound hemi-inattention)

Score Interpretation

The NIHSS Booklet published by NINDS and widely adopted clinical guidelines use the following severity categories:

• 0: No stroke symptoms
• 1 to 4: Minor stroke
• 5 to 15: Moderate stroke
• 16 to 20: Moderate-to-severe stroke
• 21 to 42: Severe stroke

Clinical Use Cases

The NIH stroke calculator serves several critical purposes in acute care:

• Triage and thrombectomy eligibility: Patients with NIHSS scores between 6 and 22 generally qualify for mechanical thrombectomy evaluation. Scores below 4 may indicate minor strokes suitable for conservative management.
• IV thrombolysis decisions: Alteplase eligibility assessments incorporate NIHSS thresholds; scores above 25 or below 4 influence the physician risk-benefit calculation for thrombolytic therapy.
• Outcome prediction: Research published in PMC (PMCID: PMC7487379) confirms that baseline NIHSS scores strongly correlate with 90-day functional outcomes, mortality, and length of hospital stay.
• Serial neurological monitoring: Repeating the assessment at 24 hours, 7 days, and 90 days quantifies neurological deterioration or improvement across the acute and subacute phases.

Worked Clinical Example

A 68-year-old patient presents with right-sided weakness and slurred speech. Clinician scores: LOC = 0, LOC Questions = 1, LOC Commands = 0, Gaze = 1, Visual = 0, Facial = 2, Left Arm = 0, Right Arm = 3, Left Leg = 0, Right Leg = 2, Ataxia = 0, Sensory = 1, Language = 1, Dysarthria = 1, Neglect = 0. Total NIHSS = 12 — classified as a moderate stroke, triggering immediate advanced imaging and thrombectomy evaluation per institutional protocol.

Factors Affecting Assessment and Interpretation

Accurate NIHSS administration depends on several clinical considerations. Language barriers and communication disorders may affect the validity of consciousness questioning and language assessment items, necessitating adjustments by experienced clinicians. Patients with pre-existing conditions such as baseline dementia, aphasia from prior strokes, or visual impairments require careful evaluation to distinguish acute deficits from chronic baseline impairments. In the hyperacute setting with extreme time pressure, clinicians prioritize rapid core assessment while documenting examination circumstances that may influence score interpretation. Serial NIHSS measurements across 24 hours, 7 days, and discharge provide temporal trends that often carry greater prognostic value than any single assessment point.

Reliability and Validation

The NIHSS demonstrates strong inter-rater reliability with weighted kappa values above 0.69 across trained examiners. Clinical decision-support research using NIHSS scores validates the scale's predictive power for discharge destination and long-term disability, reinforcing its role as the global standard for acute stroke severity quantification.