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Ranked Differential Diagnosis From a Case
Paste a case and get a differential with the can't-miss diagnoses first, the likely ones ranked, and the test that best separates them.
River's differential diagnosis builder reads a clinical case and returns a structured differential. Diagnoses that must not be missed come first, each with the feature that keeps it on the list and the test that would exclude it. Then the most likely diagnoses are ranked, with the features for and against each, followed by a prioritized next step for the workup.
It is a reasoning aid for clinicians and learners, not a diagnosis. It works only from the findings you give and says which missing finding would change the ranking most. If the case sounds like an emergency, it says so first. Ask for references and it cites only sources it actually retrieved.
This is for students and residents practising case presentations, and clinicians who want a second pass against premature closure.
Building Strong Differentials
Strong differential diagnosis starts with systematic symptom analysis. List key features of presentation: main symptom, associated symptoms, timing, context, risk factors, and relevant negatives. Then generate possible diagnoses that could explain this constellation of findings. Think broadly initially, then narrow based on likelihood. Consider common diagnoses first (when you hear hoofbeats, think horses not zebras), but don't forget serious diagnoses you can't afford to miss (life-threatening or time-sensitive conditions). For chest pain, acute MI must be on differential even if likelihood seems low.
Rank your differential by probability. List most likely diagnosis first, followed by other reasonable possibilities in descending order of likelihood. For each diagnosis, note supporting features (what fits) and opposing features (what doesn't fit). Example: 'Pneumonia: supports = fever, cough, abnormal lung sounds; opposes = no infiltrate on CXR, symptoms only 1 day.' This structured thinking helps you evaluate each possibility fairly and identify which diagnosis best explains all findings. It also helps you know what additional testing you need to confirm or exclude diagnoses.
Good differentials are dynamic. As you gather more information (additional history, exam findings, test results), your differential should evolve. Diagnoses move up or down the list. Some drop off entirely. New possibilities emerge. Document your differential at key decision points. This shows your thinking process, helps learners, and lets the next clinician see which possibilities you considered. Avoid premature closure (latching onto first diagnosis that comes to mind). Keep differential broad initially, narrow it thoughtfully with evidence, and always ask 'what else could this be?'
How it works
Paste the case
Age, sex, symptoms, timing, vital signs, exam and results so far, with identifiers removed.
Get the differential
Can't-miss diagnoses first, then likely ones ranked, with the evidence for and against each.
Refine in chat
Add a new finding or result and ask how the ranking changes, or ask for references.
What you get
- Can't-miss diagnoses listed first, each with the test that would exclude it
- Likely diagnoses ranked, with the features for and against each one
- The missing finding that would most change the ranking
- A prioritized next step for the workup, with references on request
Common questions
What is a differential diagnosis?
A differential diagnosis (DDx) is the list of possible conditions that could explain a patient's symptoms and findings, organized roughly by likelihood and urgency. Clinicians use it to structure their reasoning and decide which tests or evaluations will help confirm or rule out each possibility. It is a clinical reasoning and learning aid, not a substitute for professional medical judgment.
How do you create a differential diagnosis?
A differential diagnosis is typically built by gathering the history, symptoms, and exam findings, then listing candidate conditions and organizing them by likelihood and by "must-not-miss" severity. Frameworks such as anatomic or systematic mnemonics help ensure breadth, and further testing narrows the list. This tool is intended to support learning and clinical reasoning, not to provide medical advice or a definitive diagnosis.
How many diagnoses should be on differential?
Typically 3-6 diagnoses for most presentations. Include most likely possibilities and must-not-miss diagnoses even if less likely. Very broad differentials (15+ diagnoses) become unwieldy and don't help prioritize. Very narrow differentials (1-2 diagnoses) risk premature closure. Find balance between comprehensive thinking and practical focus. As you narrow down with testing, differential naturally becomes shorter.
How do I rank diagnoses by likelihood?
Consider epidemiology (what's common?), patient risk factors, how well the diagnosis explains all findings, and clinical experience. Common diagnoses should rank high unless features strongly suggest otherwise. Compare each possible diagnosis to the full clinical picture. Which explains the most findings with fewest assumptions? That's likely top of differential. Use clinical prediction rules and decision support tools when available. Trust clinical judgment developed through experience.
What are must-not-miss diagnoses?
Life-threatening or time-sensitive conditions that require immediate consideration even if probability is lower. For chest pain: acute MI, aortic dissection, pulmonary embolism, tension pneumothorax. For headache: subarachnoid hemorrhage, meningitis, increased ICP. For abdominal pain: ruptured AAA, ectopic pregnancy, perforated viscus. These diagnoses carry high morbidity/mortality if missed and may require urgent intervention. Keep them on radar even when other diagnoses seem more likely.
How does differential diagnosis relate to clinical decision-making?
Your differential guides diagnostic workup. Tests you order should help confirm or exclude diagnoses on differential. If pneumonia is on differential, chest X-ray makes sense. Treatment decisions also stem from differential. If you can't yet narrow to one diagnosis, you might treat empirically for most likely possibilities. Document your differential and reasoning. This shows thoughtful clinical decision-making and helps others understand your thought process if they're taking over care.
Can patients use this for their own symptoms?
No. It is built for clinicians and learners working a case, and it cannot examine anyone. If you are worried about your own symptoms, contact your doctor, and for chest pain, trouble breathing, signs of stroke or any other emergency, call emergency services. If a pasted case sounds like an emergency, the response says so before anything else.
Ranked Differential Diagnosis From a Case
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