A positive D-dimer indicates the presence of an abnormally high level of cross-linked fibrin degradation products in your body. It tells your doctor that there has been significant clot (thrombus) formation and breakdown in the body, but it does not identify the location or cause. An elevated D-dimer may be due to a VTE or DIC but it may also be due to a recent surgery, or trauma, infection, liver or kidney disease, pregnancy and diseases of pregnancy such as eclampsia, heart disease, and some cancers. A normal D-dimer test means that it is most unlikely you have an acute blood clot or disease causing abnormal clot formation and breakdown. Most doctors agree that a negative D-dimer is most valid and useful when the test is done on patients that are considered to be low-risk. The test is used to help exclude a clot as the cause of symptoms. D-dimer is recommended as an ‘additional test’. It should not be the only test used to diagnose a disease or condition. Both increased and normal D-dimer levels may require follow-up and can lead to further testing. Anticoagulant therapy can cause a false negative D-dimer. There are several different methods of testing for D-dimer. Most of the D-dimer tests that yield quantitative results are done in a hospital lab, while those that yield qualitative results are performed at the patient’s bedside. D-dimer concentrations may rise in the elderly, and false positives may be seen with high levels of rheumatoid factor (a protein seen in patients with rheumatoid arthritis). Substances such as lipaemia (a large amount of fats in the blood that can be caused by consuming a greasy meal prior to testing), and raised bilirubin can also cause false positives as can haemolysis (rupturing of red blood cells) caused by improper collection and handling. Diagnosing recurrent venous thromboembolic disease of the legs is more difficult than diagnosing a first episode of DVT. Patients who have had an initial DVT are often left with some degree of post-phlebitic syndrome, which can mimic the symptoms of recurrent disease. Duplex ultrasound often remains abnormal after a DVT, making the distinction between recurrent disease and old disease problematic. D-dimer measurement, which is elevated with thromboembolic events, is quite sensitive for the detection of initial DVT. Although not very specific, its sensitivity is such that a negative D-dimer has good negative predictive value. Since imaging studies are problematic for diagnosing recurrent disease, the D-dimer assay should be quite useful in helping to rule out recurrent DVT. This study from Oklahoma, published in the December 7 Annals of Internal Medicine, investigated the utility of a negative D-dimer assay in excluding recurrent venous thromboembolism. Three hundred consecutive patients with suspected recurrent DVT had D-dimer levels assessed. Those with negative results (<48 mcg/ml) did not undergo any further diagnostic testing. Those with positive results underwent compression ultrasound imaging. For three months after initial presentation, patients were followed up with imaging studies if there were any symptoms of recurrent DVT or PE, and also clinically at three months. Of the 300 patients, 166 had positive D-dimer studies; one half of these had negative ultrasound studies, one third had positive studies and the remainder were inconclusive. Of the 300 patients, 134 (45%) had negative D-dimer studies and did not undergo duplex scanning. In this D-dimer negative group, 11 patients returned for symptoms of recurrent thromboembolism. Of these, there were two cases of documented thromboembolism (one DVT and one PE); 4 patients had negative diagnostic tests and 5 had inconclusive studies. There was one death in the D-dimer negative group, a sudden death, which may have been a myocardial infarction. Thus, the rate of documented recurrent thromoembolism was 2/134 (1.5%). Including the sudden death and the 5 inconclusive studies, the recurrence rate was 8/134 (6%).