@inproceedings{wang-etal-2026-post,
title = "Can Post-Training Turn {LLM}s into Good Medical Coders? An Empirical Study of Generative {ICD} Coding",
author = "Wang, Ziqing and
Li, Weihao and
Chen, Shijie and
Luo, Yuan and
Ding, Kaize",
editor = "Lee, Hung-Yi and
Dev, Sunipa and
Li, Jessy and
Elliott, Desmond",
booktitle = "Findings of the {A}ssociation for {C}omputational {L}inguistics: {EMNLP} 2026",
month = oct,
year = "2026",
address = "Budapest, Hungary",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2026.findings-emnlp.459/",
pages = "9643--9658",
ISBN = "979-8-89176-462-0",
abstract = "Automated International Classification of Diseases (ICD) coding is a core medical-coding task for billing, epidemiology, and clinical decision support. Generative large language models (LLMs) are often reported as weak medical coders, but this finding mainly comes from inference-time settings such as prompting, retrieval, reranking, or tool use; the role of task-specific post-training has received limited systematic study. We present a controlled empirical study of post-training for generative ICD coding, comparing discriminative baselines with LLM coders across prompting, supervised fine-tuning (SFT), and reinforcement learning (RL) under a common protocol and metric set. To our knowledge, this is the first comprehensive controlled study of post-training for generative ICD prediction. We further introduce Progressive Hint Injection (PHI), a diagnostic missed-code curriculum within Group Relative Policy Optimization (GRPO) training. Our results show that prompting-only evaluation substantially underestimates the potential of LLMs for ICD coding. SFT provides the main capability jump, GRPO further improves code-set prediction beyond SFT, and PHI provides targeted gains on macro-level performance. These findings suggest that the main bottleneck is not the generative formulation alone, but how the model is adapted and optimized for full-taxonomy recall. We release our code, data splits, and checkpoints at \url{https://anonymous.4open.science/r/LLM4ICD}."
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<abstract>Automated International Classification of Diseases (ICD) coding is a core medical-coding task for billing, epidemiology, and clinical decision support. Generative large language models (LLMs) are often reported as weak medical coders, but this finding mainly comes from inference-time settings such as prompting, retrieval, reranking, or tool use; the role of task-specific post-training has received limited systematic study. We present a controlled empirical study of post-training for generative ICD coding, comparing discriminative baselines with LLM coders across prompting, supervised fine-tuning (SFT), and reinforcement learning (RL) under a common protocol and metric set. To our knowledge, this is the first comprehensive controlled study of post-training for generative ICD prediction. We further introduce Progressive Hint Injection (PHI), a diagnostic missed-code curriculum within Group Relative Policy Optimization (GRPO) training. Our results show that prompting-only evaluation substantially underestimates the potential of LLMs for ICD coding. SFT provides the main capability jump, GRPO further improves code-set prediction beyond SFT, and PHI provides targeted gains on macro-level performance. These findings suggest that the main bottleneck is not the generative formulation alone, but how the model is adapted and optimized for full-taxonomy recall. We release our code, data splits, and checkpoints at https://anonymous.4open.science/r/LLM4ICD.</abstract>
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%0 Conference Proceedings
%T Can Post-Training Turn LLMs into Good Medical Coders? An Empirical Study of Generative ICD Coding
%A Wang, Ziqing
%A Li, Weihao
%A Chen, Shijie
%A Luo, Yuan
%A Ding, Kaize
%Y Lee, Hung-Yi
%Y Dev, Sunipa
%Y Li, Jessy
%Y Elliott, Desmond
%S Findings of the Association for Computational Linguistics: EMNLP 2026
%D 2026
%8 October
%I Association for Computational Linguistics
%C Budapest, Hungary
%@ 979-8-89176-462-0
%F wang-etal-2026-post
%X Automated International Classification of Diseases (ICD) coding is a core medical-coding task for billing, epidemiology, and clinical decision support. Generative large language models (LLMs) are often reported as weak medical coders, but this finding mainly comes from inference-time settings such as prompting, retrieval, reranking, or tool use; the role of task-specific post-training has received limited systematic study. We present a controlled empirical study of post-training for generative ICD coding, comparing discriminative baselines with LLM coders across prompting, supervised fine-tuning (SFT), and reinforcement learning (RL) under a common protocol and metric set. To our knowledge, this is the first comprehensive controlled study of post-training for generative ICD prediction. We further introduce Progressive Hint Injection (PHI), a diagnostic missed-code curriculum within Group Relative Policy Optimization (GRPO) training. Our results show that prompting-only evaluation substantially underestimates the potential of LLMs for ICD coding. SFT provides the main capability jump, GRPO further improves code-set prediction beyond SFT, and PHI provides targeted gains on macro-level performance. These findings suggest that the main bottleneck is not the generative formulation alone, but how the model is adapted and optimized for full-taxonomy recall. We release our code, data splits, and checkpoints at https://anonymous.4open.science/r/LLM4ICD.
%U https://aclanthology.org/2026.findings-emnlp.459/
%P 9643-9658
Markdown (Informal)
[Can Post-Training Turn LLMs into Good Medical Coders? An Empirical Study of Generative ICD Coding](https://aclanthology.org/2026.findings-emnlp.459/) (Wang et al., Findings 2026)
ACL