D-dimer

D-dimer tests are ordered, along with other laboratory tests and imaging scans, to help rule out, diagnose, and monitor diseases and conditions that cause hypercoagulability, a tendency to clot inappropriately.  One of the most common of these conditions is DVT (Deep Vein Thrombosis), which involves clot formation in the deep veins of the body, most frequently in the legs.  These clots may grow very large and block blood flow in the legs, causing swelling, pain, and tissue damage.  It is possible for a piece of the clot to break off (this broken piece is called an embolus) and travel to other parts of the body, where the clot can cause a PE (Pulmonary embolus or embolism - blood clot in the lungs).

While clots most commonly form in the veins of the legs, they may also form in other areas as well; for example, clots in coronary arteries are the cause of myocardial infarction (heart attacks). Clots may also form on the lining of the heart or its valves, particularly when the heart is beating irregularly (atrial fibrillation) or when the valves are damaged. Clots also may form in large arteries as a result of damage from atherosclerosis (sometimes called hardening of the arteries). Pieces of such clots may also break off and cause an embolus that blocks an artery in another organ, such as the brain (causing a stroke) or the kidneys. Measurements of D-dimer can also be used to detect clots in these other sites.

Measurements of D-dimer may also be ordered, along with other tests, to help diagnose DIC (Disseminated Intravascular Coagulation). DIC is a complex acute condition that can arise from a variety of situations including: some surgical procedures, septic shock, poisonous snake bites, liver disease, and postpartum (after the delivery of a baby). With DIC, clotting factors are activated and then used up throughout the body. This creates numerous minute blood clots and at the same time leaves the patient vulnerable to excessive bleeding. Steps are taken to support the patient, while the underlying problem is addressed, and the underlying condition resolved. D-dimer levels may be used to monitor the effectiveness of DIC treatment.

D-dimer may be ordered when a patient has symptoms of DVT, such as leg pain, tenderness, swelling, discoloration, edema; or symptoms of PE, such as labored breathing, coughing, and lung-related chest pain.  D-dimer is especially useful when the doctor thinks that something other than DVT or PE is causing the symptoms. It is a quick, non-invasive way for the doctor to help rule out abnormal or excess clotting.

 

When a patient has symptoms of DIC, such as bleeding gums, nausea, vomiting, severe muscle and abdominal pain, seizures and oliguria (decreased urine output), a D-dimer test may be ordered, along with a PT, aPTT, fibrinogen, and platelet count to help diagnose the condition. D-dimer may also be ordered at intervals when a patient is undergoing treatment for DIC to help monitor its progress.

A positive D-dimer indicates the presence of an abnormally high level of 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 tell 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, trauma, or infection. Elevated levels are also seen with liver disease, pregnancy, eclampsia, heart disease, and some cancers.

 

A normal D-dimer test means that it is most likely that you do not have an acute condition or disease that is 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 rule out clotting as the cause for the symptoms.

D-dimer is recommended as an adjunct 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 high triglycerides, lipemia (a large amount of fats in the blood that can be caused by the patient consuming a greasy meal prior to testing), and bilirubin can also cause false positives as can hemolysis caused by improper collection and handling.