NIH Stroke Scale (NIHSS)
Standardized 15-item assessment of ischemic stroke severity. Total range 0–42.
Updated · Methodology
About this calculator
The NIHSS (National Institutes of Health Stroke Scale) is the standard for stroke severity assessment. Developed by Brott et al. (Stroke, 1989), revised 1994. Fifteen items: level of consciousness, gaze, visual fields, facial palsy, limb strength, ataxia, sensation, speech, dysarthria, neglect. Sum 0-42. Severity interpretation. 0 – no deficit. 1-4 – minor stroke. 5-15 – moderate. 16-20 – moderate-severe. 21-42 – severe. Clinical use. Standardized assessment in stroke centers. Thrombolysis decision with alteplase – NIHSS 4-25 within 4.5 hours of symptom onset (AHA/ASA 2019), with caution at NIHSS >25 (hemorrhagic transformation risk). NIHSS >=6 in the first 24 hours after anterior circulation ischemic stroke – criterion for endovascular thrombectomy in the up-to-24-hour window (DAWN, DEFUSE-3). Prognosis. Each additional admission NIHSS point raises the risk of poor functional outcome (mRS 3-6) by 24%. NIHSS 0-5 – >80% chance of functional independence at 90 days; NIHSS >20 – <30%. NIHSS is tracked every 4-6 hours in the first 24 hours, then daily. Limitations. Overestimates deficit in left-sided strokes (dominant hemisphere) due to aphasia, underestimates right-sided (less neglect captured). Does not fully assess cerebellar and brainstem function – some posterior circulation patients have NIHSS=0 with severe deficits (e.g., isolated truncal ataxia, Wallenberg syndrome). In patients with prior neurologic deficit NIHSS is hard to interpret – baseline mRS is needed.
Source
Formula version: brott-1989-aha-2019-v1
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