D-Dimer

What is the purpose of the test?

D-dimer tests are employed to exclude the existence of an abnormal blood clot (thrombus). They are particularly useful in ruling out conditions such as:

1. Deep vein thrombosis (DVT)
2. Pulmonary embolism (PE)
3. Stroke

This test serves to assess the need for additional diagnostic procedures in cases involving diseases and conditions characterized by hypercoagulability, where the blood has a propensity for inappropriate clot formation. Additionally, D-dimer levels can aid in diagnosing disseminated intravascular coagulation (DIC) and monitoring the effectiveness of treatment for DIC.

When is this test typically recommended?

D-dimer testing is typically recommended in the following situations:

1. Emergency Room Visits: D-dimer tests are often ordered when an individual presents with severe symptoms like chest pain and breathing difficulties, especially in an emergency room setting.
2. Deep Vein Thrombosis (DVT) Suspected: When a person displays symptoms suggestive of DVT, such as leg pain or tenderness, leg swelling (edema), or leg discoloration, a D-dimer test may be recommended.
3. Pulmonary Embolism (PE) Suspected: D-dimer testing may be advised when someone exhibits symptoms indicative of PE, including sudden shortness of breath, laboured breathing, coughing with blood in sputum, chest pain related to the lungs, or a rapid heart rate.
4. Assessment of Conditions Causing Hypercoagulability: It can help determine if further testing is necessary for conditions associated with abnormal blood clotting (hypercoagulability), other than DVT or PE. This includes diseases and conditions that can cause inappropriate clot formation.
5. Diagnosis and Monitoring of Disseminated Intravascular Coagulation (DIC): In cases where DIC is suspected, which may manifest as bleeding gums, nausea, vomiting, severe muscle and abdominal pain, seizures, or decreased urine output, a D-dimer test, along with other coagulation tests, may be recommended for diagnosis. It may also be periodically ordered during DIC treatment to monitor progress.

It's important to note that while D-dimer testing is valuable for ruling out abnormal clotting as a potential cause of symptoms, it should not be relied upon solely when there is a high clinical suspicion of PE. In such cases, clinical assessment takes precedence.

What should I do before the test?

D-dimer tests typically do not necessitate any special preparation, such as fasting, before undergoing the test. However, it's advisable to consult with your healthcare provider or testing facility to confirm if there are any specific instructions they would like you to follow.

How can the test be interpreted?

A normal or "negative" D-dimer result, with a level below a predefined threshold, suggests that it is highly likely that the individual being tested does not have a current condition or disease that is causing abnormal clot formation and breakdown.

D-dimer test results may be reported in units of milligrams per liter (mg/L) fibrinogen equivalent units (FEU). As per the American Board of Internal Medicine, a negative D-dimer level falls below 0.50 mg/L FEU, while a positive result indicates a level above 0.50 mg/L FEU.

In the medical community, there is general consensus that a negative D-dimer result is most valuable and reliable when the test is conducted on individuals who are considered to have a low to moderate risk of thrombosis (abnormal blood clot formation). The primary purpose of the test is to help rule out clot-related causes of symptoms.

On the other hand, a positive D-dimer result may suggest the presence of an abnormally high concentration of fibrin degradation products. This indicates that there might be significant formation and breakdown of blood clots (thrombi) within the body, but the test does not provide information about their location or cause. For instance, this elevation could be due to venous thromboembolism (VTE) or disseminated intravascular coagulation (DIC), with D-dimer levels typically markedly elevated in cases of DIC.

Nonetheless, an elevated D-dimer result does not conclusively indicate the presence of a clot, as various other factors can lead to increased levels. Elevated D-dimer levels may be observed in conditions where fibrin is formed and subsequently broken down, such as after surgery, trauma, infection, heart attacks, or certain cancers, or in conditions where fibrin is not effectively cleared, like in liver disease.

Therefore, D-dimer is typically not employed to exclude VTE in hospitalized patients in an inpatient setting.

During pregnancy, fibrin is formed and degraded, potentially resulting in elevated D-dimer levels. In cases where DIC is suspected in pregnant women or those in the immediate postpartum period, the D-dimer test may be employed in conjunction with other tests like prothrombin time (PT), partial thromboplastin time (PTT), fibrinogen, and platelet count to aid in the diagnosis. A significantly elevated D-dimer level may suggest DIC in such cases.

D-dimer is recommended as a supplementary test. Due to its high sensitivity but relatively poor specificity should be used primarily to rule out deep vein thrombosis (DVT) rather than to confirm a diagnosis. It is unsuitable for use in cases of pulmonary embolism (PE) when there is a high clinical suspicion of the condition.

Both elevated and normal D-dimer levels may necessitate further investigation and can lead to additional diagnostic tests. In cases where D-dimer tests yield positive results and individuals have a moderate to high risk of DVT, further assessment with diagnostic imaging, such as CT angiography, may be required.

When employed to monitor the progress of DIC treatment, decreasing D-dimer levels indicate the effectiveness of the treatment. In contrast, increasing levels may suggest that the treatment is not producing the desired results.