D dimer .63, negative ultrasound of leg. please explain why the test is elevated with no other reasons for elevation. should i ask for ct scan?

Elevated in lots dx: Ddimer is good screening and helpful only if negative. It is a phase reactant. It can be positive if you have even stubbed your toe (just for an example). If you have any other issues in your body that cause inflammation (arthritis, recent fall, etc) it can be abnormal. If you are at high risk for major blood clot CT scan can test for that otherwise, no other testing is recommended just b/c.

Unremarkable : First off there are multiple reasons for d dimer elevations other than a DVT or pe. Also- the number you quoted (63) to my knowledge is not considered to be a positive result for the test. Ct scan of the chest is a good test if you have suspicion for a pulmonary embolus or if you have a very hight risk score. If symptoms are minimal and risk is minimum then you are likely ok without a ct scan.