PURPOSE: Intrinsic capacity (IC), a crucial indicator for the United Nations Decade of Healthy Ageing 2021-2030, is defined by WHO as the foundation of functional ability, representing the composite of all physical and mental capacities of an individual. IC spans five function domains: Locomotor, psychological, cognitive, vitality, and sensory (including vision and hearing). Accurate IC assessment is vital for effective interventions, yet comparative analyses of these tools are scarce. Consequently, we evaluated the diagnostic accuracy of three IC assessment tools in individuals aged 80 and above-Integrated care for older people (ICOPE) Step 1, ICOPE Step 2, and the Lopez-Ortiz's IC scoring system. PATIENTS AND METHODS: This cross-sectional analysis included a total of 475 participants aged ≥80 years between July 2023 and January 2024 in 11 nursing homes in Ningbo, Zhejiang Province, China. To assess that included sociodemographic and health-related information alongside the three IC tools. Diagnostic efficacy was gauged using sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), accuracy, Youden index, and the area under the curve (AUC). RESULTS: The detection of IC decline exceeded 85% across all methods. Using ICOPE Step 2 as a benchmark, ICOPE Step 1 showed robust performance across four domains of locomotion, psychological, cognitive, and vitality, whereas the Lopez-Ortiz's IC scoring system was generally ineffective. CONCLUSION: All three IC assessment methods have limitations. To save resources, ICOPE Step 1 can be considered for direct assessment in non-sensory domains. Conversely, the ICOPE Step 2 and Lopez-Ortiz's IC scoring systems exhibited overly stringent and lenient thresholds, respectively. At this stage, IC assessment tools cannot balance subjectivity and objectivity; thus, it is recommended that the appropriate tool be selected according to actual application scenarios. Continuous improvement of IC assessment tools remains a requirement for future studies.