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Pretest Probability

Use a pulmonary embolism case to practice Bayesian thinking, likelihood ratios, and test threshold decisions.

Page 1: Chief Complaint: Coughing of blood

Choose a pretest probability, reveal a positive D-dimer, update your estimate, and decide whether to order CTPA.

Page 2: Updating probabilities in medicine

Frame clinical reasoning as moving from a prior estimate to an updated probability after new evidence.

Page 3: Likelihood Ratios

Introduce LR+ and LR- as tools for translating test results into changed probability.

Page 4: Likelihood Nomogram

Adjust pretest probability and likelihood ratio to see how post-test probability changes.

Page 5: Nomogram for our Patient

Apply the nomogram to the patient from the first page.

Page 6: Follow-up

See how the CTPA decision and updated probability translate into the patient outcome.