Elevated D-dimer levels usually indicate the presence of a blood clot which is in the process of being broken down though it does not indicate the site(s) of the clot(s). I don't know of any evidence which links it to rheumatoid arthritis.

Iodine contrast can lead to kidney problems though this is rare. It can also lead to thyroid gland problems (either hyperthyroidism or hypothyroidism). I can not find any evidence linking it to auto-immune diseases.