Assessing the Limitations of Large Language Models in Clinical Practice Guideline-Concordant Treatment Decision-Making on Real-World Data: Retrospective Study.

Background: Studies have shown that large language models (LLMs) are promising in therapeutic decision-making, with findings comparable to those of medical experts, but these studies used highly curated patient data. Objective: This study aimed to determine if LLMs can make guideline-concordant treatment decisions based on patient data as typically present in clinical practice (lengthy, unstructured medical text). Methods: We conducted a retrospective study of 80 patients with severe aortic stenosis who were scheduled for either surgical (SAVR; n=24) or transcatheter aortic valve replacement (TAVR; n=56) by our institutional heart team in 2022. Various LLMs (BioGPT, GPT-3.5, GPT-4, GPT-4 Turbo, GPT-4o, LLaMA-2, Mistral, PaLM 2, and DeepSeek-R1) were queried using either anonymized original medical reports or manually generated case summaries to determine the most guideline-concordant treatment. We measured agreement with the heart team using Cohen κ coefficients, reliability using intraclass correlation coefficients (ICCs), and fairness using the frequency bias index (FBI; FBI >1 indicated bias toward TAVR). Results: When presented with original medical reports, LLMs showed poor performance (Cohen κ coefficient: -0.47 to 0.22; ICC: 0.0-1.0; FBI: 0.95-1.51). The LLMs' performance improved substantially when case summaries were used as input and additional guideline knowledge was added to the prompt (Cohen κ coefficient: -0.02 to 0.63; ICC: 0.01-1.0; FBI: 0.46-1.23). Qualitative analysis revealed instances of hallucinations in all LLMs tested. Conclusions: Even advanced LLMs require extensively curated input for informed treatment decisions. Unreliable responses, bias, and hallucinations pose significant health risks and highlight the need for caution in applying LLMs to real-world clinical decision-making.