Real-world performance of open-source large language models in diabetes diagnosis.

Background: This study aimed to evaluate the performance of diverse open-source large language models (LLMs) in diagnosing diabetes subtypes and comorbidities from unstructured clinical text, assessing the impact of model characteristics, prompting, and language. Methods: We conducted a retrospective analysis of 11,329 adult diabetes patients from a large Chinese tertiary center (2010-2020). Various open-source LLMs were tested using four prompting strategies in English and Chinese. Primary outcomes were F1-scores for multi-class diabetes subtyping and binary classification of diabetic kidney disease (DKD) and metabolic syndrome (MetS). Results: LLMs demonstrated high performance in complex subtyping (peak F1 0.951) but showed limitations in rule-based DKD (F1 0.570) and MetS (F1 0.650) diagnosis. Chain-of-Thought prompting improved MetS classification but degraded DKD performance. Optimal model size was approximately 32B parameters. Notably, English prompts outperformed Chinese prompts on native Chinese text. Conclusion: Open-source LLMs exhibit strong holistic pattern recognition for complex classification but struggle with rule-based procedural reasoning. These models are promising as clinical co-pilots to augment expert decision-making rather than serving as autonomous diagnostic tools.