What are the pathology tests for Deep Vein Thrombosis (DVT)?

From the Guidelines

DVT diagnosis should start with D-dimer testing as the initial screening test, followed by compression ultrasonography as the gold standard imaging test for confirmation, as recommended by the American Society of Hematology 2018 guidelines 1. The diagnosis of deep vein thrombosis (DVT) requires a step-wise approach, starting with an assessment of clinical probability using standardized clinical prediction rules, such as the Wells score or Geneva score 1.

• For patients with low clinical probability, D-dimer testing can be used as the initial test to reduce the need for diagnostic imaging 1.
• A negative D-dimer result can effectively rule out DVT in low-risk patients, while a positive result requires confirmation with imaging 1.
• Compression ultrasonography is the gold standard imaging test, offering high sensitivity and specificity for proximal DVT without radiation exposure 1.
• For patients with suspected pulmonary embolism or when ultrasound is inconclusive, CT venography or MR venography may be used 1. Key considerations in DVT diagnosis include:
• The use of clinical prediction rules to estimate the clinical probability of VTE 1
• The selection of diagnostic tests based on the clinical probability of VTE 1
• The importance of confirming DVT diagnosis with imaging tests, such as compression ultrasonography or CT venography 1
• The need for thrombophilia testing and other laboratory tests in certain cases, such as unprovoked DVT or recurrent events 1. In terms of specific tests, D-dimer testing is recommended as the initial screening test, followed by compression ultrasonography as the gold standard imaging test 1. Other tests, such as complete blood count, coagulation studies, and thrombophilia testing, may be recommended in certain cases, particularly for unprovoked DVT, recurrent events, or family history of clotting disorders 1. Renal and liver function tests are also important before starting anticoagulants to guide medication selection and dosing 1. Overall, the diagnosis of DVT requires a comprehensive approach that takes into account clinical probability, diagnostic testing, and laboratory results, with the goal of reducing morbidity, mortality, and improving quality of life for patients with VTE 1.

From the FDA Drug Label

The primary efficacy endpoint, venous thromboembolism (VTE), was a composite of documented deep vein thrombosis (DVT) and/or documented symptomatic pulmonary embolism (PE) reported for up to 24 days following randomization.

Table 7. Efficacy of Fondaparinux Sodium in the Peri-operative Prophylaxis of Thromboembolic Events Following Hip Fracture Surgery

Endpoint	Peri-operative Prophylaxis (Day 1 to Day 7 ± 2 post-surgery)	Fondaparinux Sodium 2.5 mg SC once daily	Enoxaparin Sodium 40 mg SC once daily
n/N	a	% (95% CI)	n/N
VTE		52/626	8.3% b (6.3,10.8)
All DVT		49/624	7.9% b (5.9,10.2)
Proximal DVT		6/650	0.9% b (0.3,2.0)

Table 8. Efficacy of Fondaparinux Sodium in the Extended Prophylaxis of Thromboembolic Events Following Hip Fracture Surgery

Endpoint	Extended Prophylaxis (Day 8 to Day 28 ± 2 post-surgery)	Fondaparinux Sodium 2.5 mg SC once daily	Placebo SC once daily
n/N	a	% (95% CI)	n/N
VTE		3/208	1.4% b (0.3,4.2)
All DVT		3/208	1.4% b (0.3,4.2)
Proximal DVT		2/221	0.9% b (0.1,3.2)

The FDA drug label does not answer the question about DVT pathology tests. The label provides information about the efficacy of fondaparinux sodium in preventing venous thromboembolism (VTE) and deep vein thrombosis (DVT) in patients undergoing hip fracture or hip replacement surgery, but it does not discuss pathology tests for DVT. 2

From the Research

DVT Pathology Tests

• The diagnosis of deep vein thrombosis (DVT) requires a multifaceted approach that includes clinical assessment, evaluation of pre-test probability, and objective diagnostic testing 3.
• Common symptoms and signs of DVT are pain, swelling, erythema, and dilated veins in the affected limb 3.
• The pre-test probability of DVT can be assessed using a clinical decision rule that stratifies DVT into "unlikely" or "likely" 3, 4, 5, 6.

Diagnostic Tests

• If DVT is "unlikely", a D-dimer test can be used to exclude DVT 3, 4, 5.
• If the D-dimer level is normal, DVT can be excluded; if the D-dimer level is increased, compression ultrasound can be used to confirm the diagnosis 3, 4, 5.
• Compression ultrasonography (CUS) can confirm DVT in patients with a high clinical probability of DVT 3, 4, 5.
• A rapid automated enzyme-linked immunoabsorbant assay (ELISA) D-dimer test can be used to rule out ongoing venous thromboembolic processes 4.

Clinical Prediction Rules

• A clinical prediction rule can be used to help decide about starting anticoagulant therapy while awaiting ultrasound examination 6.
• The clinical prediction rule comprises four risk factors for DVT (personal history of venous thromboembolism, immobilization in previous month, estrogen contraceptive, active malignancy), one clinical sign (swelling of the calf), and the presence of an alternative diagnosis more likely than that of DVT 6.

Cost-Effectiveness Analysis

• A cost-effectiveness analysis of four strategies for diagnosing DVT found that combining clinical probability and D-dimer with a single ultrasound in the diagnostic workup of patients with possible DVT is highly cost-effective 7.
• The most expensive strategy was serial ultrasound, while the least expensive and most cost-effective option was to perform D-dimer as the initial test, followed by a single ultrasound if the D-dimer level was abnormal 7.