The aim of this study was to compare the two methodological approaches recommended in ICRP Publication 135 for establishing regional diagnostic reference levels (DRLs), by applying them to a common multicountry dataset from the Optimisation of Protection in Pediatric Interventional Radiology in Latin America and the Caribbean (OPRIPALC) programme. A retrospective methodological analysis was conducted using radiation dose data collected between December 2020 and December 2023 from centres participating in OPRIPALC. After applying predefined inclusion criteria, data cleaning and trimming in accordance with ICRP-135 recommendations, 1684 paediatric interventional cardiology procedures from 11 centres in eight countries were included. Kerma area product (PKA) was selected as the primary dosimetric quantity. Regional DRLs were derived using two approaches: Method A, based on the 75th percentile of pooled patient level PKA data, and Method B, based on the 75th percentile of centre specific median PKA values assumed to represent typical country values. DRLs were established using predefined age and weight groups. Both methodologies preserved the expected increase in DRL values with patient age, weight and procedural type. However, Method A consistently produced higher regional DRL values than Method B, particularly for therapeutic procedures and higher age or weight categories. These differences reflect the effects of data aggregation rather than differences in the underlying dataset. This study aims at illustrating the practical implications of one method over the other, rather than to recommend one methodology over the other. The findings highlight the importance of methodological transparency in regional DRL initiatives and support the applicability of the OPRIPALC framework for paediatric interventional cardiology in other regions.