I have prolonged qt syndrome. i have had pain in my leg for months since i foot surgery. i asked my doctor on monday to test my d-dimer. it was 456ng. what does this mean?

Normal range: The normal range for D-dimer is approximately 0.5 mg/l of blood or 500 mg/ml of blood. All laboratory results need to be interpreted in the clinical context and the doctor who ordered the tests is usually in the best position to do that. Talk to the doctor who ordered the tests. Having said that, it more or less rules out deep vein thrombosis.

Biomechanics: Sometimes, depending on the type of foot surgery you have had, the biomechanics of walking are changed and the way you are walking is not the same. You may be striking the ground with more pressure which would lead to more shock to the tibia and fibula (bones of the leg) and cause some long term pain and maybe a shin splint. See the doctor who performed the surgery and address the changes.