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RheumBench: A Specialist-Validated Rubric-Based Benchmark for Evaluating Large Language Models in Rheumatology

Lechner F, Bamberger J, Kremer P, Richter J, Schneider M, Kiltz U, Kuhn S, Flek L et al.

2026

Abstract

Abstract Large language models (LLMs) are increasingly used for clinical decision support, yet scalable and specialty-specific methods for evaluating their performance and safety remain limited. We developed RheumBench, the first rubric-based LLM benchmark in rheumatology, providing a specialist-validated framework for open-ended evaluation. We evaluated ten systems, comprising three frontier proprietary general-purpose LLMs, one frontier open-weight general-purpose LLM, and six clinical retrieval-augmented generation (RAG) systems, including two certified medical products and one rheumatology-specific RAG system. RheumBench comprised 100 clinical cases (70 diagnostic and 30 diverse clinical management) and 1,020 case-specific rubric criteria independently reviewed and weighted for clinical appropriateness and potential harm by two board-certified rheumatologists. Systems were evaluated for answer quality, prompt sensitivity, potential harm, diagnostic accuracy, and system confidence. Responses were scored by a three LLM judge panel, yielding 50,553 rubric-level LLM evaluations, with high agreement with rheumatologist consensus (Cohen’s κ = 0.91). Overall system performance (0-100%) varied substantially, with a maximum RheumBench score of 54.0% (Claude Fable 5), and frontier general-purpose LLMs generally outperformed clinical RAG systems, including certified Prof. Valmed and DR.INFO. Management case performance varied widely, with thorough prompting improving mean…

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