MedAction: Towards Active Multi-turn Clinical Diagnostic LLMs

• URL: http://arxiv.org/abs/2605.07305v1
• Date: Fri, 08 May 2026 06:15:24 GMT
• Title: MedAction: Towards Active Multi-turn Clinical Diagnostic LLMs
• Abstract summary: Existing medical training data teaches models to reason from complete information but not to act under evolving, partial evidence.<n>We introduce MedAction, a tree-structured distillation pipeline that synthesizes diverse and high-quality multi-turn diagnostic trajectories.<n>Using this pipeline, we construct MedAction-32K, a dataset of 32,681 trajectories from 2,896 PMC cases.
• Score: 11.709211007913803
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Most existing LLM diagnoses are evaluated on static, single-turn settings where complete patient information is provided upfront, an oversimplification of real clinical practice. We study active diagnosis: the real-life clinical process of starting from initial observation, ordering tests, interpreting results, and updating a differential diagnosis across multiple turns. Through systematic analysis, we identify three recurring failure modes in current LLMs: ungrounded test ordering, unreliable diagnostic update, and degraded multi-turn coherence. Together, these failures reveal a core deficit: existing medical training data teaches models to reason from complete information but not to act under evolving, partial evidence. To address this gap, we introduce MedAction, a tree-structured distillation pipeline that synthesizes diverse and high-quality multi-turn diagnostic trajectories via LLM-environment interaction. We propose two knowledge-graph-grounded metrics to filter trajectory quality: Disease Trajectory Consistency (DTC), which tracks whether the model's hypothesis converges toward the correct diagnosis, and Reasoning-Action Consistency (RAC), which verifies that belief updates are driven by gathered evidence. Using this pipeline, we construct MedAction-32K, a dataset of 32,681 trajectories from 2,896 PMC cases. Fine-tuning an 8B model on MedAction-32K achieves state-of-the-art performance among open-source models on both MedR-Bench and our curated MedAction-300-Hard benchmark, pushing the edge for open-source medical LLMs.

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