What does blood clot in the lungs (pulmonary embolus) show on ventilation perfusion scan?

Lack of blood flow. A ventilation perfusion scan is a test for a blood clot in the lungs, or pulmonary embolism. If there is a blood clot, an area of the lung will not be perfused, but will be ventilated, and therefore a mismatch will be seen.
Typical. The typical finding is a mismatch between ventilation and perfusion, however in people with small clots or underlying pulmonary disease the findings are the scan are not always clear.
Sometimes unclear. The findings of a ventilation perfusion scan can sometimes be non-specific and unhelpful. The better way to confirm a pe now is with a spiral ct scan of the lungs with infusion.
Mismatch. Normal ventilation and decreased perfusion, that is normal air but blocked blood flow by clots.
Various. Typically a pulmonary embolism will show defects on the perfusion portion of a ventilation/perfusion scan (also know as a vq).