Figure 3a: Use of GCPs to achieve clinical resolution (solid lines = positive result, dashed lines = negative result). Posttest probability for a positive result is derived by drawing a vertical line up to the solid curved line and then across to the y-axis. Posttest probability for a negative result is derived by drawing a vertical line up to the dotted curved line and then across to the y-axis. (a) GCP for D-dimer test. For a patient with a high pretest probability of PE, the prevalence is 78% (solid arrow). Posttest probability for a positive D-dimer result is 85% (open arrow), which warrants further investigation. (b) This posttest probability is then applied as pretest probability to the GCP for CT pulmonary angiography (solid arrow). If the result is positive, posttest probability is 99% (open arrow) and PE is confirmed. If the result is negative, posttest probability is 30% (curved arrow), which is not low enough to exclude disease (further investigation warranted). (c) This posttest probability is then applied as pretest probability to the GCP for indirect CT venography (solid arrow). If the result is positive, posttest probability of DVT is greater than 72% (open arrow) and diagnosis is confirmed. If the result is negative, posttest probability of DVT is less than 5% (curved arrow) and the diagnosis is excluded.