A 38-year-old female has been immobilized for 4 months and shows signs of PE but a VQ scan does not confirm it. What is the next diagnostic test?

In the context of suspected pulmonary embolism (PE) where the ventilation-perfusion (V/Q) scan did not confirm the diagnosis, pulmonary angiography is the next logical step for definitive diagnosis. This test is often referred to as the "gold standard" for diagnosing PE, as it directly visualizes the pulmonary arteries and can identify any occlusions or abnormalities that may indicate the presence of an embolism.

CT angiography is indeed a commonly used and effective non-invasive option for diagnosing PE; however, pulmonary angiography is more direct and definitive, particularly in cases where patients have inconclusive results from preliminary tests like the V/Q scan.

While an ultrasound of the legs can be helpful in assessing for deep vein thrombosis (DVT), which is a common source of PE, it does not directly evaluate the pulmonary vasculature. A chest X-ray is useful for ruling out other conditions but lacks the specificity and sensitivity needed to assess for pulmonary embolism.

Hence, in a clinical scenario where a patient shows signs of PE but preliminary imaging does not confirm it, pulmonary angiography becomes the preferred next step for diagnosis.