BACKGROUND: There is a tremendous clinical and research need to bridge the gap between disorder of consciousness and functional independence scales with a single unidimensional measure in people with acquired brain injury. AIM: To calibrate an essentially unidimensional subset of items from the Italian Early Functional Abilities (EFA), demonstrating internal construct validity and sufficient reliability for individual patient measurement. DESIGN: Multicenter observational cross-sectional study. SETTING: Inpatients from 11 different Italian Rehabilitation centers. POPULATION: Three hundred sixty-two adult patients with a disorder of consciousness due to an acquired brain injury. METHODS: The Italian version of EFA was administered to the sample and then submitted to Mokken analysis, Confirmatory Factor Analysis, Rasch analysis, Confirmatory Bifactor Analysis, and external construct validity. RESULTS: According to Mokken Analysis (all item scalability coefficients Hj positive; all item-pair scalability coefficients Hij >0.3; scale coefficient H=0.762), and Confirmatory Factor Analysis (RMSEA=0.081; SRMR=0.048; CFI=0.995; TLI=0.995), the Italian EFA showed a sufficient preliminary unidimensionality. Within Rasch Analysis, a final 12-item solution for the EFA (EFA-R) was calibrated. EFA-R is “essentially unidimensional” according to the following requirements: 1) analysis of residual correlations which supported item essential local independence; 2) a robust correlation between item subtests (rho=0.950); 3) only 2.1% of cases with significant difference between person parameter estimates by different subscales; 4) an explained common variance equal to 0.916 obtained from a final Confirmatory Bifactor Analysis. It also satisfied invariance requirement (unconditional χ2₂₀=9.81; P=0.457, conditional class-interval based χ2₃₅=33.1; P=0.557), and monotonicity. The reliability (Person Separation Index=0.887) was adequate for person measurements. A practical raw-score-to-measure conversion table based on the EFA-R calibration was devised. Finally, EFA-R strongly correlated with Coma Recovery Scale-Revised (rho=0.922) and motor FIM™ (rho=0.808). CONCLUSIONS: EFA-R is an essentially unidimensional subset of 12 items with adequate internal construct validity and sufficient reliability for individual patient measurement under the Rasch Model Theory framework. CLINICAL REHABILITATION IMPACT: EFA-R has the potential to measure people’s functional abilities whose consciousness is improving despite ongoing severe motor-functional impairments during the early stages of rehabilitation. It provides “a measurement bridge” between the disorder of consciousness and the functional independence scales in patients with severe acquired brain injury.