Cost effective approach for emergency department investigation of deep vein thrombosis

• d-dimer
• deep vein thrombosis
• plethysmography
• pretest

I read with interest the paper by Kilroy et al.¹ Wells’ criteria of pretest probability (PTP) has recently been validated in a large randomised control trial² for excluding pulmonary embolism. Kilroy et al¹ admit that using PTP the risk stratification was successful, it was not quite as discriminatory as Wells’ original data.

Wells’ study² has important implications for practice because it shows that combination of a low PTP, and a negative d-diner test safely excluded pulmonary embolism in outpatients, obviating further investigations in 40% of patients.² However, the occurrence of deep vein thrombosis in up to 20% of patients with a “high” PTP score and negative d-dimer test emphasises the point that the d-dimer test cannot be used in isolation.²

SimpliRED d-dimer assay in the study by Kilroy et al¹ had a low sensitivity. All d-dimer assays differ and clinicians should know the diagnostic performance of the test used in their own institutions.

Compression ultrasonography is by no means a cheap investigation as the authors perceive.¹ Plethysmography can be used as an alternative investigation for the diagnosis of deep vein thrombosis. Digital photoplethysmography can be used as an useful cheap tool to exclude deep vein thrombosis safely in an emergency department, thus reducing pressure on the radiology department.³ Table 1 shows the tesults of a study using computed strain gauge plethysmography.

Based on our experience we would like to conclude that we can fulfil our assumption of good practice by achieving a negative predictive value of 100% by combining PTP, a modern d-dimer test, and either digital photoplethysmography or computed strain gauge plethysmography to exclude deep vein thrombosis in an emergency department. However, we believe further randomised control trials are necessary to test this hypothesis.