D-dimer and calf circumference in the evaluation of outpatient deep venous thrombosis

Duplex ultrasonography (DU) is the primary method for diagnosis of deep venous thrombosis (DVT) but is relatively expensive and not always readily available. Attempts to exclude the diagnosis of DVT with D-dimer or clinical criteria independently have been unsuccessful. The goal of our study was to evaluate a second-generation rapid quantitative D-dimer and simple clinical parameters for screening of outpatients for DVT.

Patients undergoing DU of the lower extremities for suspected DVT were prospectively evaluated. Patients undergoing lower extremity venous ultrasound scan for suspected pulmonary embolism or already on anticoagulant therapy were excluded from the study. Data were analyzed to assess the optimal combination of characteristics to include and exclude proximal DVT.

One hundred fifty-six outpatients met inclusion criteria and were enrolled in the study. Elevated levels of D-dimer of 0.5 ng/mL or more were noted in 21 of 22 patients diagnosed with DVT, yielding a sensitivity of 95% and negative predictive value of 99%. Subjective symptoms of swelling or pain were present in 94% of all outpatients. Asymmetric calf swelling of more than 2.0 cm was noted in 14 of 22 patients (64%) with proximal DVT compared with 22 of 134 patients (16%) without DVT (P <.003). No single clinical history variable was significant on multivariate analysis. All outpatients with proximal DVT had either leg swelling of more than 2 cm or a positive D-dimer.

A combination of a second-generation quantitative D-dimer and calf measurement provides an easy and effective means of excluding proximal DVT when screening outpatients. Patients with calf circumference 2.0 cm or less and a negative D-dimer may undergo nonemergent DU. Patients with a positive D-dimer or asymmetrical calf swelling of more than 2.0 cm alone or in combination should undergo emergent DU.