Peripheral Venous Testing and Interpretation: DVT and Venous Insufficiency
Core Concepts
Venous duplex relies on compressibility, augmentation, phasicity, and valve competence. For deep vein thrombosis (DVT), the primary criterion is non-compressibility; secondary signs include intraluminal echogenicity, absent or diminished phasicity with respiration, loss of augmentation, and collateral flow. Understand the difference between acute and chronic thrombus: acute is hypoechoic, dilates the vein, and is non-compressible; chronic is echogenic, contracted, with recanalization and collaterals.
Venous Insufficiency
Reflux testing uses provocation (Valsalva for femoral, distal compression for popliteal and calf). Know normal valve closure times (commonly <0.5 s for deep veins and <0.5 s for superficial veins, though thresholds vary by lab). Understand the role of perforators and superficial systems.
Traps
Frequent traps: calling a vein non-compressible when the transducer pressure is inadequate or the patient is tense; mistaking slow flow for thrombus; and ignoring isolated calf vein thrombosis. Another trap is interpreting absent phasicity as DVT when it can reflect proximal obstruction elsewhere or extrinsic compression. Also, do not diagnose reflux without proper provocation and patient positioning.
Worked Example
A patient has a popliteal vein that does not compress, is hypoechoic, and shows no augmentation. This supports acute DVT. The trap would be to call it chronic because of mild echogenicity-acute thrombus can be slightly echogenic early. Correlate with vein diameter and collaterals.
Rule of Thumb
Compressibility is the cornerstone: if the vein fully compresses, DVT is unlikely at that site. For reflux, require reproducible reversal exceeding the lab threshold with adequate provocation.