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Importance of Pretest Probability Score and D-Dimer Assay Before Sonography for Lower Limb Deep Venous Thrombosis

¹ Academic and Research Division, Department of Radiology, Waikato Hospital, Hamilton, New Zealand.
² Department of Radiology, Waikato Clinical School, University of Auckland, Hamilton, New Zealand.
³ Present address: Department of Medical Imaging, The Canberra Hospital and the Australian National University, Canberra, Australia.
⁴ Department of Haematology, Waikato Hospital, Hamilton, New Zealand.

OBJECTIVE. The purpose of our study was to develop and validate a clinical score (the Hamilton score) for the assessment of lower limb deep venous thrombosis (DVT) and to determine the usefulness of this score and a D-dimer assay before a complete lower limb sonographic examination.

SUBJECTS AND METHODS. Five hundred forty-two consecutive ambulatory patients presenting to the emergency department were prospectively recruited, of whom 16 patients were excluded from the study. Eighteen history and examination variables were collected by the emergency department physicians. The Simplify D-dimer assay and a complete, single lower limb sonographic examination were performed in all patients. All patients with a negative sonographic examination for DVT were followed up for 3 months, and all those with a positive sonographic examination were given anticoagulation therapy. The Hamilton score was developed using the data from the first 214 patients and was prospectively validated in the next 312 patients.

RESULTS. The most significant factors associated with a diagnosis of DVT were immobilization of the lower limb, active malignancy, and a strong clinical suspicion of DVT without other diagnostic possibilities by the emergency department physicians. Other factors were bed rest or recent surgery, male sex, calf circumference difference greater than 3 cm, and erythema. The Hamilton score was developed with the following weights: immobilization of the lower limb (2 points), active malignancy (2 points), strong clinical suspicion of DVT without other diagnostic possibilities by the emergency physicians (2 points), bed rest or recent surgery (1 point), male sex (1 point), calf circumference difference greater than 3 cm (1 point), and erythema (1 point). A score of 3 or greater indicates a likely probability for DVT, and a score of 2 or less represents an unlikely probability for DVT. Of the 103 patients with an unlikely probability Hamilton score and a negative D-dimer assay, only one patient had isolated calf DVT. A combined diagnostic strategy of unlikely-probability Hamilton score and a negative D-dimer would have a negative predictive value of 99% (95% confidence interval, 94.7–100%).

CONCLUSION. An unlikely-probability Hamilton score and a negative Simplify D-dimer assay effectively exclude lower limb DVT, and a sonographic examination is unnecessary in this group of ambulatory emergency department patients.

Keywords: deep venous thrombosis • Hamilton score • Simplify D-dimer assay • sonography • veins

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