Pre-test probability
Also called Prior probability
Pre-test probability is how likely a condition is before a test, based on age, sex, risk factors and symptoms. It decides how much a result should move you.
Why it matters in a workup
The same normal result means different things at different pre-test probabilities. In a high-probability patient it may not exclude the condition.
Write down the probability you started from, even roughly. It makes the reasoning behind your next step visible.
Put it into practice
- Estimate it from the history and risk factors
- Record it before interpreting the test
- Explain results that contradict it
Frequently asked questions
Does a normal test always lower the probability?
It lowers it, but by how much depends on the test and where you started. A very likely condition can survive a normal result.
General guidance on clinical documentation, not advice about any individual patient and not legal advice.
Glossary
Look up related terms
- Clinical reasoningClinical reasoning is how a clinician gathers information, weighs it and reaches a diagnosis and plan, including the checks against common errors.
- Differential diagnosisA differential diagnosis is a ranked list of the conditions that could explain a patient's problem, with the reasoning for each position.