Could an ultrasound scan miss a dvt as iam at high risk of a dvt and is 422 high for a d dimer test?

Ultrasound for DVT: Ultrasound for lower extremity DVT's have great sensitivity and specificity meaning they are very good at picking up a DVT. There is a 2% chance of somebody having a negative scan and having one found 1 week later according to studies, although repeating it is often done if there is strong suspicion. D-dimer values are not universal so that may be high but values can be high in a lot of disease.

Unlikely, and yes.: The scan is unlikely to miss a significant leg clot. It could miss a pelvic vein clot as the study is not an efficient means to evaluate those vessels. Regarding the d-dimer level it is elevated but there reasons other than venous thrombosis for a high value.