Although D-Dimers are frequently used to assist (along with other diagnostics, ie, vq scan, CT Scan, ultrasound etc.) in identification of DVT's, Pulmonary Embolism etc. Alone this test is essentially nonspecific and may become elevated for numerous reasons aside from blood clots. For example, other conditions in which elevations may occur are due to fever, infection, recent trauma or surgical procedures in the previous three months, malignancy, etc. A D-Dimer is essentially a product of clotting so in answer to your question, "So you could have a normal d-dimer but still have a dvt that is older. Is this true, or will the d-dimer be elevated no matter how old the clot is"? It is highly unlikely that this result would be normal if a clot was present. In my opinion, it would be much more likely to show an elevation in this case or in any of the above examples previously mentioned. Identification of a DVT would not be based soley on an elevation or lack of for that matter of a D-Dimer test but would be included along with other diagnostics, symptoms, etc., and a diagnosis would be based on the picture as a whole.
Theresa Jones, RN