Background: In Western countries, an incidence of deep vein thrombosis (DVT) in the lower limb is roughly 2.5-5%. If left
untreated, this conditon carrys a significant mortality rate due to pulmonary embolism (PE) as well as an increase in morbidity due to chronic venous insufficiency and venous ulceration., In Thailand, the rate of incidence has not, as of yet been established. Though, DVT is not an uncommon disease . A known gold standard test, for DVT is duplex ultrasonography,
which with its sensitivity and specificity is more than 95% accurate. Negative aspects of this test are expense, technically
demands, time-consuming and not widely available. As an alternative, the digital photoplethysmography (D-PPG) can be a
simple, non-invasive, reliable and non-operator device that can effectively test screen in the diagnosis of DVT.
Objective: To determine the role of digital photoplethysmography (D-PPG) and the optimum cut off-point of venous refilling time (RT) and venous pumping (VP) in the diagnosis of DVT when compared with duplex ultrasonography.
Material and Method: Prospective study of 80 patients (127 swelling limbs) where clinical manifestations of DVT was suspected in lower limbs. Each patient was assessed by D-PPG and duplex ultrasonography.
Results: In 80 patients, 127 limbs were found to have had swelling of the lower limbs and 50 limbs had DVT as demonstrated by duplex ultrasonography. Using RT with a range of 19-21 second intervals as the optimal cut-off point, D-PPG achieved a sensitivity rate of 94%, a negative-predictive value of 92%, a specificity of 58%, and a positive-predictive value of 52%.
Conclusion: These results were validated by using D-PPG as a useful screening device in the diagnosis of patients with swelling limbs who were clinically suspected of contracting DVT of the lower limb. Patients who tested positive (for DVT) required further confirmation by duplex ultrasonography, where as a negative result (via RT >21s) excluded DVT.

Keywords: Deep vein thrombosis, Digital photoplethysmography, sensitivity and specificity