Aim: To examine the effect of implementing the Patient Complexity Instrument (PCI) in addition to usual-care on complexity detection, clinical-care time allocation, and referrals to supportive services compared to usual-assessment alone.Design: A parallel-group-blocked pragmatic randomised controlled trial.Methods: A mixed-method study conducted within a regional Australian community nursing service. Randomisation occurred at the initial client assessment following referral acceptance for community nursing support. Older people aged 65 years and over (client participants), referred to the service from 1st of July 2020 to 30th of September 2020, eligible for Commonwealth-Home-Support-Programme funding. A convenience sample of community nurses conducting client-assessments were recruited. The intervention group included usual-assessment plus the PCI and the control group was usual-assessment alone. Chi-square test independence compared complexity ratings (low, medium, high) between groups for the hypothesis that adding the PCI to usual-assessment, has no effect on nurses’ complexity detection compared to usual-assessment alone.Results: Compared to usual-assessment alone, adding the PCI did not change nurses’ level detected complexity rating. However, for older people initially assessed with low levels of complexity, the PCI indicated a need for additional clinical-care-time. The nurses feedback showed the PCI useful in prompting to identify other care factors such as level of engagement, psychosocial which were not identified by usual-assessment alone thus, enhanced complexity detection.Conclusion: The addition of PCI to nurses’ usual-assessment did not improve levels of complexity ratings. However, the PCI enhanced complexity detection by pinpointing areas of care requiring referrals for additional care and extra-time required. The ImPaCt trial demonstrated the PCI as a useful tool for enhancing care for older people receiving nursing supports in the community. The PCI is a beneficial guidance resource for those new to Community Nursing role caring for older people.Key words: district or community nurse, older people, ageing, care complexity, clinical decision-making, clinical judgement, quality of care, assessment, community aged-care.ImpactWhat problem did the study address? The trial addresses the limited evidence and use of standardised tools for detecting care complexity and greater dependence on nurses’ clinical judgment for people living in the community.    What were the main findings? The trial highlighted that the PCI could enhance community-based care for complex older people, and serves as a valuable guide for elder care, especially for those new to the community nurse role.  Where and on whom will the research have an impact?