Hack's Impairment Index (HII)

Used to quantify global neuropsychological impairment from the Halstead–Reitan battery to classify normal vs. mild/moderate/severe brain dysfunction. Indicated in adults undergoing evaluation for suspected brain injury, cognitive decline, or neuropsychological deficit; provides a quick composite severity score aiding diagnostic stratification. Cross‑validation shows ~60–66% severity agreement with established deficit scales 1 [Level III evidence].

Provides rapid neurologic status quantification but has limited validation and modest discrimination in perioperative cohorts. Derived from small, heterogeneous samples and not validated for surgical decision-making. Does not capture frailty, cardiopulmonary reserve, or comorbidity burden, so it risks miscalibration when applied broadly. Should be used only as a supplement to clinical judgment, echoing cautions from perioperative risk-tool evidence showing frequent miscalibration in contemporary patients 1 [Level III evidence].