Medical Feature Extraction From Clinical Examination Notes: Development and Evaluation of a Two-Phase Large Language Model Framework

Background Medical feature extraction from clinical text is challenging because of limited data availability, variability in medical terminology, and the critical need for trustworthy outputs. Large language models (LLMs) offer promising capabilities but face critical challenges with hallucination. Objective This study aims to develop a robust framework for medical feature extraction that enhances accuracy by minimizing the risk of hallucination, even with limited training data. Methods We developed a two-phase training approach. Phase 1 used instructing fine-tuning to teach feature extraction. Phase 2 introduced confidence-regularization fine-tuning with loss functions penalizing overconfident incorrect predictions, which were captured using bidirectional matching targeting hallucination and missing features. The model was trained using the full data of 700 patient notes and on few-shot 100 patient notes. We evaluated the framework on the United States Medical Licensing Examination Step-2 Clinical Skills dataset, testing on a public split of 200 patient notes and a private split of 1839 patient notes. Performance was assessed using precision, recall, and F1-scores, with error analysis conducted on predicted features from the private test set. Results The framework achieved an F1-score of 0.968-0.983 on the full dataset of 700 patient notes and 0.960-0.973 with a few-shot subset of 100 of 700 patient notes (14.2%), outperforming INCITE (intelligent clinical text evaluator; F1=0.883) and DeBERTa (decoding-enhanced bidirectional encoder representations from transformers with disentangled attention; F1=0.958). It reduced hallucinations by 89.9% (from 3081 to 311 features) and missing features by 88.9% (from 6376 to 708) on the private dataset compared with the baseline LLM with few-shot in-context learning. Calibration evaluation on few-shot training (100 patient notes) showed that the expected calibration error increased from 0.060 to 0.147, whereas the Brier score improved from 0.087 to 0.036. Notably, the average model confidence remained stable at 0.84 (SD 0.003) despite F1 improvements from 0.819 to 0.986. Conclusions Our two-phase LLM framework successfully addresses critical challenges in automated medical feature extraction, achieving state-of-the-art performance while reducing hallucination and missing features. The framework’s ability to achieve high performance with minimal training data (F1=0.960-0.973 with 100 samples) demonstrates strong generalization capabilities essential for resource-constrained settings in medical education. While traditional calibration metrics show misalignment, the practical benefits of confidence injection led to reduced errors, and inference-time filtering provided reliable outputs suitable for automated clinical assessment applications.

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