Large language models for interpretation of health checkup results.

Large language models (LLMs) show strong generalization, yet their ability to interpret structured medical data remains insufficiently studied. This work evaluated four LLMs-Claude Sonnet 4, Gemini 2.5 Pro, GPT-4o, and LLaMA 3.1-70B-using comprehensive health checkup data from the Korean National Health Insurance Service. Multiple prompting strategies (few-shot, role-based, constraint-based, and Chain-of-Thought) were tested. Zero-shot accuracy averaged 0.69 (SD 0.06), increasing to 0.92 (0.06) with combined strategies and to 0.95 (0.07) with Chain-of-Thought. Claude Sonnet 4, Gemini 2.5 Pro, and GPT-4o achieved the highest accuracies (≥ 0.98), while LLaMA 3.1-70B showed lower but improvable performance. Item-level analysis of 10,000 cases demonstrated near-perfect accuracy (0.99-1.00) for most biochemical markers, including glucose, cholesterol, triglycerides, and liver enzymes. In contrast, blood pressure showed lower accuracy (0.61-0.91), with age-related decline, likely due to the complexity of multi-categorical thresholds requiring integration of systolic and diastolic values. Subgroup analyses revealed model-specific biases: sex-related biases were observed in body mass index (Claude Sonnet 4) and urine protein, serum creatinine, and gamma-glutamyl transferase (LLaMA 3.1-70B), while age-related biases were identified in blood pressure (Claude Sonnet 4, Gemini 2.5 Pro) and low-density lipoprotein cholesterol and hemoglobin (LLaMA 3.1-70B). Overall, advanced prompting markedly improved model performance, and top-tier LLMs demonstrated robust interpretive capability, while caution is needed for variables with complex clinical semantics such as blood pressure.