In this study, LEUS revealed a 13% incidence of DVT among patients with ischemic stroke. Female sex and a severe neurological deficit were independently associated with the presence of DVT in the acute phase of ischemic stroke. However, the usefulness of D-dimer level for screening DVT in Asian patients with acute ischemic stroke was limited. Elevated D-dimer level was observed in more than a quarter of patients with ischemic stroke, with the mechanism of stroke being particularly associated with elevated D-dimer level.
Although D-dimer level is useful for detecting DVT in other conditions such as liver disease and malignancy, several studies showed that the initial D-dimer level is not associated with the presence of DVT in stroke patients.  Ischemic stroke shows associations with thrombotic/fibrinolytic conditions, especially in the case of cardioembolic and cancer-associated strokes.  Therefore, the D-dimer level is typically increased in those with cardioembolic strokes  and is useful for detecting cancer-associated strokes.  In accord with previous studies, our results also showed that D-dimer level was associated with the stroke mechanism, with cardioembolic stroke being an independent factor associated with elevated D-dimer levels. As D-dimer is elevated in acute ischemic stroke patients and as thrombolysis and the stroke mechanism influences the D-dimer level, it may be less useful for detecting DVT in patients with acute ischemic stroke.
Instead, severe neurological deficits were associated with DVT in acute ischemic stroke patients. There was a significant difference in the NIHSS score between those with and without DVT. Especially the NIHSS score of the lower leg weakness, which directly influences the ambulation in their acute period, showed a significant difference. It is well known that immobilization or paralysis of the lower extremities is associated with DVT because of the increased venous stasis.  The prevalence of DVT or pulmonary embolism is lower in Asians than in non-Asian subjects, and coagulopathy is less associated with ischemic stroke in Asian patients. [17, 18] Therefore, the relative importance of systemic coagulopathy represented by the D-dimer level may be less important in Asian patients with ischemic stroke, and immobilization and severe neurological deficit may be more important in the development of DVT in Asian patients with acute ischemic stroke. 
The results of our study indicate that the role of D-dimer for the screening of DVT in Asian patients with acute ischemic stroke may be limited. Studies using D-dimer to screen for DVT showed a very low rate of DVT in Asian patients with acute ischemic stroke.  Therefore, the use of LEUS may be more appropriate in selected high-risk patients. LEUS for the detection of DVT also has the benefits of no radiation hazard and cost-effectiveness in comparison with computerized tomography venography. High-risk patients are those with a severe neurological deficit or immobilization, and acute ischemic stroke patients with a low D-dimer level should not be presumed to be free of DVT;  in our study, more than 60% of patients with DVT showed a normal D-dimer level. Furthermore, performing LEUS on these patients provided additional information on the size, chronicity, and degree of occlusion of the thrombus, which may help in determining the management of DVT in patients with acute ischemic stroke. However, LEUS is observer dependent and still has limitations in detecting DVT in the pelvic or calf area in comparison to computerized tomography venography.  Therefore, the evaluation for detecting DVT in acute ischemic stroke patients may be individualized.
Our study has several limitations, including those stemming from the small sample size from a single center. The LEUS was performed within 3 days from admission, which is a very early period, and the prevalence of DVT may have increased if the LEUS was performed later on after the index stroke, and the relative power of the predictors could also have been different. Furthermore, we only checked D-dimer on the day after admission, and did not make any follow-up checks. The usefulness of D-dimer at follow-up was observed in a former study.  Third, patients with distal DVT, for which the clinical implication is still controversial, were included in this study. Finally, only a limited number of patients received intermittent pneumatic compression, as it was not commonly used during the study period. The results may differ under a more aggressive care to prevent DVT in those with high risk patients.