What laboratory tests are indicated for a patient presenting with left leg pain and swelling, suspected to have Deep Vein Thrombosis (DVT)?

From the Guidelines

For a patient with left leg pain and swelling with suspected deep vein thrombosis (DVT), I would order D-dimer testing as the initial laboratory test, as recommended by the American Society of Hematology 2018 guidelines for management of venous thromboembolism: diagnosis of venous thromboembolism 1. If the D-dimer is negative, DVT is unlikely, but if positive, further imaging is needed. Some key points to consider when ordering labs for suspected DVT include:

• Complete blood count (CBC) to assess for anemia, infection, or platelet abnormalities
• Coagulation studies including prothrombin time (PT), international normalized ratio (INR), and activated partial thromboplastin time (aPTT) to evaluate clotting function and guide potential anticoagulation therapy
• Basic metabolic panel (BMP) or comprehensive metabolic panel (CMP) to assess kidney and liver function before starting anticoagulants
• Consider thrombophilia testing including Factor V Leiden, Protein C and S levels, antithrombin III, and antiphospholipid antibodies for patients with unprovoked DVT or younger patients, though these are typically done after initial management, as suggested by the American College of Chest Physicians evidence-based clinical practice guidelines 1. D-dimer is particularly useful as it measures fibrin degradation products that increase with clot formation, though it has high sensitivity but low specificity, meaning a negative result helps rule out DVT but a positive result requires confirmation with imaging studies like ultrasound, as noted in the American Society of Hematology 2018 guidelines 1.

From the Research

Diagnostic Approach for Suspected Deep Vein Thrombosis (DVT)

To diagnose DVT, a combination of clinical assessment, evaluation of pre-test probability, and objective diagnostic testing is recommended 2. The patient's symptoms, such as pain and swelling in the left leg, should be evaluated using a clinical decision rule to determine the pre-test probability of DVT.

Laboratory Tests

The following laboratory tests can be ordered to aid in the diagnosis of DVT:

• D-dimer test: This test measures the level of D-dimer in the blood, which is a protein fragment produced when blood clots are broken down. A negative D-dimer result can help rule out DVT, while a positive result indicates the need for further testing 3, 4, 5.
• Complete blood count (CBC): This test can help identify any underlying conditions that may be contributing to the development of DVT.
• Blood chemistry tests: These tests can help evaluate the patient's overall health and identify any potential underlying conditions that may be contributing to the development of DVT.
• Urinalysis: This test can help identify any underlying conditions, such as nephrotic syndrome, that may be contributing to the development of DVT 6.

Important Considerations

When ordering laboratory tests, it is essential to consider the following:

• The D-dimer test should be performed before the administration of anticoagulant therapy, such as rivaroxaban, as this can affect the test results 3.
• The clinical decision rule should be used to determine the pre-test probability of DVT, and the D-dimer test should be used in conjunction with this assessment to rule out DVT 2, 5.
• A negative D-dimer result does not completely rule out DVT, and further testing, such as compression ultrasonography, may be necessary to confirm the diagnosis 4.