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Timely Clinical Diagnosis through Active Test Selection
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Proposes ACTMED, which combines Bayesian Experimental Design with LLM-generated surrogate samples of test outcomes to adaptively select clinical tests and stop testing early, evaluated on CKD, hepatitis C, diabetes and a custom OSCE-style set.
Problem
Clinical diagnosis with ML usually relies on static fully observed datasets and ignores the sequential, cost-aware test selection clinicians perform; diagnosis must be made timely under resource limits.
Approach
Use LLMs as zero-shot generative surrogates to sample plausible hidden test outcomes and posterior disease probabilities, then pick the test maximizing expected KL divergence between posterior and prior belief (cost-normalized), with a KL-based stopping rule, without task-specific training.
Key results
- On Diabetes and Hepatitis, ACTMED with GPT-4o outperforms baselines and even the full-information LLM classifier at 3 acquired tests (e.g., hepatitis accuracy 0.839 with KL vs 0.770 entropy-based).
- KL-based stopping at gamma=0.7 reduces average tests to about 1.0-2.3 across datasets, roughly halving diagnostic burden with comparable accuracy.
- Three clinicians and two medical students rated 94.5 ± 1.4% of test selections and risk adjustments as clinically reasonable.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Replace KL-based selection with entropy-based selection (ablation) | ACTMED · Diabetes, Kidney, and Hepatitis | accuracy: Diabetes: 0.572 ± 0.005 -> 0.593 ± 0.039; Kidney: 0.972 ± 0.010 -> 0.992 ± 0.006; Hepatitis: 0.770 ± 0.010 -> 0.825 ± 0. | Helped |
| Increase stopping threshold γ from 0.3 to 0.7 (ablation) | ACTMED · Hepatitis, Diabetes, and Kidney | average tests selected: GPT-4o-mini: Hepatitis 2.36 ± 0.68 -> 1.48 ± 0.73; Diabetes 2.45 ± 0.71 -> 1.90 ± 0.74; Kidney 1.60 ± 0.75 -> 1.28 ± 0.5 | Helped |
| Use GPT-4o rather than GPT-4o-mini for surrogate sampling | LLM test-outcome surrogate · Diabetes and Hepatitis | Wasserstein distance: Diabetes: 0.117 ± 0.046 -> 0.110 ± 0.038; Hepatitis: 0.173 ± 0.237 -> 0.130 ± 0.157 | Helped |
| Use GPT-4o rather than GPT-4o-mini for surrogate sampling | LLM test-outcome surrogate · Diabetes and Hepatitis | Energy distance: Diabetes: 0.269 ± 0.094 -> 0.256 ± 0.079; Hepatitis: 0.330 ± 0.254 -> 0.265 ± 0.191 | Helped |
| Use ACTMED rather than other feature-selection baselines | Clinical diagnosis · Hepatitis C and Diabetes | diagnostic accuracy | Helped |
| Use ACTMED rather than other feature-selection baselines | Clinical diagnosis · CKD | diagnostic accuracy | No clear effect |
| Apply KL-based early stopping rather than acquiring all three selected tests | ACTMED · Hepatitis, Diabetes, and Kidney | diagnostic accuracy | Helped |
| Use KL-based early stopping rather than baseline feature selection | ACTMED · Hepatitis, Diabetes, and Kidney | number of tests: nearly 50% | Helped |
| Use ACTMED rather than implicit feature selection | Clinical diagnosis · Diabetes | personalization of test selection | Helped |
| Use ACTMED for clinician-reviewed test decisions and risk adjustments | ACTMED · Clinician-in-the-loop evaluation | clinically reasonable judgments: 94.5 ± 1.4% | Helped |
Surprising findings
- Constrained selection of three tests surpassed the full-information LLM baseline on hepatitis and diabetes, suggesting feature selection reduces noise.
- Implicit LLM selection strongly favors globally optimal features, showing limited personalization.
Limitations
- Limited dataset scale (about 1,000 patients total) and binary single-disease framing.
- Relies on strong high-capacity LLMs; smaller models fail to produce accurate surrogate samples.
- Only structured categorical and numerical features; free-text reports not incorporated.
Experimental setup
Datasets: UCI Chronic Kidney Disease UCI HCV data (Hepatitis C) Pima Indians Diabetes AgentClinic (OSCE-style cases)
Benchmarks: UCI Chronic Kidney Disease UCI HCV data (Hepatitis C) Pima Indians Diabetes OSCE-style AgentClinic dataset
Metrics: accuracy Wasserstein distance energy distance mean absolute error of sampled features average number of tests
Baselines: LLM classifier with all features Random selection Global best fixed subset Implicit LLM selection Entropy-based EIG
Builds on: Bayesian Experimental Design active feature acquisition AgentClinic
Closest papers by meaning
- MedExAgent: Training LLM Agents to Ask, Examine, and Diagnose in Noisy Clinical Environments (NeurIPS 2026 · similarity 0.86)
- Large Language Models Are Clinical Reasoners: Reasoning-Aware Diagnosis Framework with Prompt-Generated Rationales (AAAI 2024 · similarity 0.85)
- Simulating Viva Voce Examinations to Evaluate Clinical Reasoning in Large Language Models (NeurIPS 2025 · similarity 0.85)
- CMR-RD: Long-Tailed Adaptive VLM for Explainable CMR Diagnosis (CVPR 2026 · similarity 0.84)
- Aligning Evaluation with Clinical Priorities: Calibration, Label Shift, and Error Costs (NeurIPS 2025 · similarity 0.83)
- ClinicalLab: Aligning Agents for Multi-Departmental Clinical Diagnostics in the Real World (NeurIPS 2025 · similarity 0.83)
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