I had an elevated d-dimer result of 464. i had an x-ray, ct and ekg done. all came back fine. what could cause this elevation and should i be worried?

Lots of reasons: A d-dimer can be elevated for a number of reasons beyond scenarios where blood clots are involved. It is known to be elevated in pregnancy, liver disease, infections, inflammatory disease, cancers, trauma, post surgery, even with increasing age(though this shouldn't be the case with you). You should review this with your primary care doctor to make sure nothing is being missed. Best of luck.

Why all the tests?: I'm guessing you had chest pain and shortness of breath and they thought you had a blood clot to the lungs. The elevated d-dimmer indicates the presence of a clot but not location. Depending on how elevated your doc may start anti coagulation medication. If you are awake and online and under the care of a doctor there's probably not much to worry about.