The following article features coverage from the American Society of Hematology 2020 meeting. Click here to read more of Hematology Advisor‘s conference coverage.

A recently developed diagnostic algorithm was found to safely rule out deep vein thrombosis (DVT) in patients visiting an emergency department, thereby reducing the requirement for ultrasound imaging by nearly 50%, according to study results presented by Kerstin de Wit, MBChB, MDm MSc, of McMaster University, Hamilton, Ontario, Canada, at the virtual 62nd American Society of Hematology (ASH) Annual Meeting and Exposition.

“Ultrasound scan is costly and it’s also somewhat inconvenient for patients. In Canada, we have limited access to ultrasound for deep vein thrombosis after 5 PM, so we frequently have to ask patients to return the following day to the emergency department for their ultrasound scan,” explained Dr de Wit.

Furthermore, ultrasound may carry a high financial cost that can lead to delayed diagnosis of DVT. Therefore, the Designer D-dimer Deep Vein Thrombosis Diagnosis (4D) Study ( Identifier:  NCT02038530) was conducted by Dr de Wit and colleagues to assess the ability of a diagnostic algorithm to minimize the need for ultrasound imaging in patients with suspected DVT. The algorithm uses clinical pretest probability (C-PTP)-based D-dimer thresholds to exclude DVT.

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In the algorithm:

  • The 9-item Wells score was used to categorize a patient’s C-PTP as low, moderate, or high.
  • If the C-PTP was low and D-dimer was <1000 ng/mL, or if C-PTP was moderate and D-dimer was <500 ng/mL, the patient did not undergoes further diagnostic testing for DVT and did not receive anticoagulant therapy.
  • All other patients underwent proximal vein ultrasound examination.
    • If the ultrasound was negative but accompanied by very high D-dimer (thus low or moderate C-PTP with D-dimer ≥3000 ng/mL) or high C-PTP with D-dimer ≥1500 ng/mL, the patient underwent a second proximal venous ultrasound examination 1 week later.

The investigators evaluated the safety and efficiency of the 4D algorithm in a Canadian prospective multicenter management study of outpatients with potential DVT. The primary outcome was symptomatic, objectively verified venous thromboembolism (VTE; proximal DVT or pulmonary embolism), and all patients had 90 days of follow-up.

Between April 2014 and March 2020, 1512 patients with signs or symptoms of DVT (mean age, 60 years; 58% women) were enrolled in the study. In total, 173 (11%) patients were diagnosed with DVT on initial or serial diagnostic testing: 168 on the day of presentation and 5 after 1 week during the second ultrasound imaging.

Of the patients who did not have DVT according to ultrasound imaging (1298/1512; 86%), 7 were diagnosed with VTE during follow-up (0.5%; 95% CI, 0.3-1.1).

Of the 579 patients who had low (n=378) or moderate (n=201) C-PTP and D-dimer results (<1000 or <500 ng/mL, respectively), 2 were diagnosed with VTE during follow-up (0.4%; 95% CI, 0.1-1.3).

Upon follow-up, 3 of 572 patients with a single negative ultrasound and low or moderate C-PTP with D-dimer less than 3000 ng/mL (n=423) or high C-PTP with D-dimer less than 1500 ng/mL (n=149) were diagnosed with VTE (0.5%; 95% CI, 0.2-1.5).

The average number of ultrasound examinations using the 4D algorithm was 0.72, and the average number of ultrasound examinations using the conventional algorithm was 1.36, reflecting a difference of -0.64 (95% CI, -0.68 to -0.61) or a 47% relative reduction (total ultrasound scans, 1083 and 2053, respectively).

In addition, of the 1275 patients who had proximal DVT excluded and who were not treated with anticoagulants, only 8 patients were diagnosed with VTE in the subsequent 90 days (0.6%; 95% CI, 0.3-1.2).

Disclosure: Some authors have declared affiliations with or received funding from the pharmaceutical industry. Please refer to the original study for a full list of disclosures.

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de Wit K, Papira S, Schulman S, et al. Deep vein thrombosis diagnosis with D-dimer adjusted to clinical probability. Presented at: American Society of Hematology (ASH) 62nd Annual Meeting and Exposition; December 5-8, 2020. Abstract 429.