Abstract Background/Aims Accurate diagnostic coding has the potential to support effective outpatient paediatric rheumatology care, enabling reliable service evaluation and monitoring. We sought to describe the current state of diagnostic coding across paediatric rheumatology care providers in England, aiming to improve the understanding of the paediatric rheumatology case mix. Methods Data were extracted from the Hospital Episode Statistics Outpatient dataset (HES-OP) for all encounters coded to Rheumatology or Paediatric Rheumatology for individuals aged ≤17 years across two financial years (2023/24 and 2024/25). Primary diagnostic information for each encounter was recorded using International Classification of Diseases, 10th Revision (ICD-10) codes. Codes and their definitions were reviewed before codes were grouped into rational categories. Where diagnostic coding data were missing, a default code (R69X - Unknown and unspecified causes of morbidity) is automatically assigned. Encounters with this diagnostic code were considered evidence of missing diagnostic data. Results A total of 174,337 encounters, representing 41,143 patients across 127 providers, were identified. 145,848 (83.7%) encounters had missing diagnostic data. Approximately one quarter of individual patients (10,174, 24.7%) had at least one encounter with a coded diagnosis during the study period. A total of 901 unique ICD-10 codes were used, which were rationally grouped into 60 categories. The five most frequent diagnostic categories, with example codes, are summarised in the Table. Most providers (104/127, 81.9%) had no diagnostic coding data for any encounter, including nine of the 16 commissioned providers. Of the 23 providers with diagnostic coding, the mean proportion of coded encounters was 29.9% (standard deviation 27.0, range 0.1-78.1%). Conclusion There is a widespread lack of accurate and consistent diagnostic coding for outpatient paediatric rheumatology activity. Where coding is performed, there is variation in the codes used, which poses challenges to understanding case mix and benchmarking activity across sites. Future work will explore the processes of diagnostic coding in specific sites in greater detail and will inform recommendations for standardised diagnostic coding processes across providers. These findings highlight the urgent need for system-wide improvements to outpatient diagnostic coding, an essential foundation for the data-driven improvement of outpatient care pathways. Disclosure R.D. Sandler: None. W.K. Gray: None. G. Cleary: None. L. Martin: None. L.J. Kay: None. P.C. Lanyon: None. F. McErlane: None.
Sandler et al. (2026) studied this question.