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Objectives A growing number of national diagnostic reference levels based on clinical indications (NDRL ci) in CT have been implemented worldwide since the International Commission on Radiological Protection’s 2017 recommendation. This study aims to compare NDRLci practices, identify influencing factors and propose evidence-based recommendations for NDRLci development, based on the literature published between 1996 and 2025.Design Systematic review.Setting A systematic literature search was conducted in PubMed, Web of Science and Scopus from 1996 to 24 august 2025. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis framework was followed to report the study selection process in this review. Joanna Briggs Institute’s critical appraisal tools were used to evaluate the articles critically.Participants Adult patients undergoing CT scans for various clinical indications.Intervention Clinical indication-based CT protocols with reported NDRL ci values as CT dose index volume and dose length product (DLP).Primary and secondary outcome measures The primary outcomes were NDRL ci values reported for various clinical indications. The secondary outcomes were CT technology, protocol parameters and patient characteristics influencing NDRLci.Result A total of 4146 articles were identified. 410 full texts were examined and 11 studies were included in the systematic review. 25 clinical indications across seven anatomical regions were identified across 11 included studies. The NDRL ci for urinary stones and cerebrovascular accident had the highest number of references, while flank pain and occlusion had the lowest number. The highest NDRLci in DLP was found for total body CT in severe trauma (3830 mGy cm) and the lowest for sinusitis (70 mGy cm).Conclusion Several factors contribute to dose discrepancies for the same clinical indications in CT imaging, including kilovolt peak and milliampere-second, scan length, number of phases, patient size, reconstruction algorithm, CT scanner age and specifications, underscoring the need for standardised and optimised CT protocols. This review highlighted several challenges, which emphasise the importance of international organisations to standardise the development of NDRL ci to improve comparability across countries.PROSPERO registration number CRD42024603574.