Doppler ultrasound is used in the diagnosis of varicose veins. The lower limb veins are able to be assessed easily with ultrasound. A downside is that the results differ depending on the examiner’s skill, the testing method, and the recording method. To derive standardized testing methods and results, it will be necessary to prepare examination guidelines based on clinical research and practical expe-rience. We aim to produce evidence-based standard recommendations based on key questions from reported data, rather than individual experience. Some parts with a shortage of comparative research or excessive debate were excluded. However, for some fields with high clinical significance and where the opinions of experts were consistent, even in the absence of sufficient evidence in the literature, recommendations were prepared based on a consensus using the nominal group technique. In this review, we prepared recommendations for the definition of reflux, which is a main aspect of ultrasound diagnosis of varicose veins (Table 1).

Table 1 . Key Question 5. What are the criteria for positive reflux in each target vessels in varicose veins?.

Recommendation	Strength of recommendation	References
5-1. At least 0.5 second of reflux is considered a positive result for the great saphenous vein (GSV), anterior/posterior accessory saphenous veins (AASV/PASV), small saphenous vein (SSV), perforating vein, tibial vein, and deep femoral vein.	Strong	1-15
5-2. At least 1.0 second of reflux is considered a positive result for the common femoral vein, femoral vein, and popliteal vein.	Strong	4, 8, 9, 16
5-3. Reticular veins, spider veins, and telangiectasias are commonly observed even in the absence of reflux in the saphenous veins, and their clinical significance in the measurement of reflux under ultrasound has not yet been demonstrated. As such, ultrasound diagnostic criteria for these conditions are not presented.	Insufficient	17-21

5-1. At least 0.5 second of reflux is considered a positive result for the great saphenous vein (GSV), anterior/posterior accessory saphenous veins (AASV/PASV), small saphenous vein (SSV), perforating vein, tibial vein, and deep femoral vein

The diagnosis of varicose veins is achieved by diagnosing reflux due to valve insufficiency. It is recommended to assess reflux in all veins of the lower limb, including not only the deep veins, the great saphenous vein (GSV), and the small saphenous vein (SSV), but also accessory saphenous veins, and the perforating vein (1). When testing for reflux due to venous insufficiency, the test is performed with the patient standing, and, either the Valsalva maneuver is used to increase abdominal pressure and induce reflux in the proximal veins, or a hand or toniquet is used to apply pressure and induce reflux in the distal veins. After applying pressure to the calf using a hand, the reflux are examined while releasing the pressure (2). Although the international consensus was previously to observe reflux for at least 0.5 s irrespective of the type of vein (3), the threshold for reflux in the femoral and popliteal veins is 1 s, in the GSV, SSV, tibial vein, and deep femoral vein is 0.5 s (2,4,5), and, likewise, 0.5 s is considered reflux in the other superficial truncal veins, including the anterior accessory saphenous vein (AASV) (6). In previous guidelines, the threshold for reflux in the perforating vein was 0.35 s (7). According to clinicians, at least 0.5 s of reflux is defined as a positive result, and many clinical guidelines and documents define perforating vein insufficiency as at least 0.5 s of reflux after applying pressure to the calf (4,8,9).

Labropoulos et al. (2) studied ultrasound to assess 80 lower limbs in 40 healthy volunteers and 60 lower limbs in 45 chronic venous disease patients. At least 0.5 s of abnormal reflux in the GSV, SSV, tibial vein, or deep femoral vein could be taken as a standard for reflux. The analysis included a total of 273 perforating veins from healthy volunteers, and the duration of reflux flow in the perforating vein, irrespective of location, was measured between 0 and 0.76 s (mean, 0.17 s), but reflux was less than 0.35 s in 97% of perforating veins. In particular, the reflux duration was longer for perforating veins in the calf than in the thigh (mean, 180 ms [95% CI, 176∼184] vs 150 ms [95% CI, 145∼155]; p<0.0001). Among the patients, there were 71 out of 312 perforating veins showing a reflux duration of at least 0.5 s. Using a threshold of 0.35 s, 82 perforating veins could be diagnosed with reflux. Although an arbitrary threshold of 0.5 s has been used to date, this study suggests that the definition of reflux for the perforating vein could be lowered to 0.35 s. Based on this study, Labropoulos et al. (10) performed follow-up research using a threshold of 0.35 s for reflux in the perforating vein.

Nevertheless, there is still debate about the definition of reflux in the perforating vein, and research is ongoing, including studies on the vein diameter. In Doppler ultrasound, generally, pathologic reflux can be considered when the reflux waveform is over 0.35 s, the vein diameter is over 3.5 mm, and especially, when accompanied by skin lesions (2,11). Sandri et al. (11) reported that the diameter was greater than 3.5 mm in over 90% of cases of perforating vein insufficiency, and the SVS/AVF guidelines define pathologic perforating vein as cases with at least 0.5 s of reflux, at least 3.5 mm diameter, and skin ulcers (12) Labropoulos et al. (13) diagnosed perforating vein insufficiency when the diameter was at least 3.9 mm under ultrasound, and reported a sensitivity of 73% and specificity of 96%. However, in one-third of cases of perforating vein accompanied by reflux, the diameter was less than 3.9 mm. Moreover, since the diameter of the perforating veins differs depending on the location, irrespective of reflux, it is difficult to diagnose perforating vein insufficiency based on diameter. We do not recommend diagnosing reflux based on only vein diameter under ultrasound, but rather using the reflux duration (1,4,5).

Labropoulos recently elucidated the characteristics of the perforating veins (14). They reported that, although the perforating vein diameter was small and reflux could be defined as 0.35 s in their study, a threshold value of 0.5 s could simply be used for superficial veins. In varicose veins, perforating veins can also dilate to handle the increased blood flow over time, and as the disease progresses, the connecting perforating veins can also show varicose changes (10). Primary reflux in the perforating veins has not been observed when the superficial veins are competent, and all cases of reflux in perforating veins are reported to be associated with reflux in superficial veins. In addition, bidirectional flow is observed in the perforating veins of healthy individuals without varicose veins. As such, reflux can be defined as reflux flow exceeding 0.5 s (net outward flow >500 ms) (15).

5-2. At least 1.0 second of reflux is considered a positive result for the common femoral vein, femoral vein, and popliteal vein

Regarding the minimum value of 1.0 s for reflux in the femoral and popliteal veins, this is the definition that has been used in several previous guidelines and studies. This committee will continue using this value without modifications (4,8,9,16).

5-3. Reticular veins, spider veins, and telangiectasias are commonly observed even in the absence of reflux in the saphenous veins, and their clinical significance in the measurement of reflux under ultrasound has not yet been demonstrated. As such, ultrasound diagnostic criteria for these conditions are not presented

Several researchers have attempted to investigate the relationship between reticular veins and telangiectasias accompanied by Doppler reflux (17-19). The researchers reported that telangiectasias, which are connected, via small perforating veins around the knee, in a superficial reticular venous network that drains into the deep veins, could be a separate venous system from the saphenous veins. As such, the pathophysiological mechanisms causing clinical symptoms such as saphenous vein insufficiency appear to have a different cause from telangiectasias. In the Edinburgh Vein Study, there was no clear causal relationship between saphenous vein reflux and telangiectasias (20). Instead, increasing telangiectasia severity was associated with increasing frequency and severity of varicose veins. The majority of clinicians have considered that, in this case, resolving varicosity of the saphenous veins is a precondition to the successful management of telangiectasias. However, 51.4% of severe telangiectasia patients and 75.7% of mild telangiectasia patients do not have accompanying saphenous vein insufficiency, suggesting that the two pathophysiological systems are different (20). The Edinburgh Vein Study showed that there was no symptomatic and anatomical relationship between the saphenous system and the reticular network, which supplies blood to telangiectasia. Varicose veins and telangiectasias shows similar symptoms that typically co-occur. We are not aware of any scientific research regarding the effects of treating one system on the other system, or of any evidence suggesting which system to treat first. This is a topic where randomized clinical studies should be conducted. The European guidelines for sclerotherapy (21) report that, while there is a trend for using Doppler ultrasound to examine telangiectasias and reticular veins before treatment, CW-doppler alone may be sufficient (recommendation 13, grade 1C. European guidelines for sclerotherapy). Nevertheless, when anatomical or hemodynamic examination is required, such as in cases of recurrent varicose veins or vascular malformation, Doppler ultrasound must be performed before sclerotherapy (recommendation 14, grade 1B).

Chronic venous disease can have various presentations, and the extent of varicose veins, symptoms, and reflux differ between patients. Treatment decisions must, above all, be based on the patient’s symptoms. However, it is also important to check for reflux when choosing the treatment method. Nevertheless, when inappropriate treatment is selected due to concerns about recurrence or the therapeutic effects, it can lead to an increase in medical expenses and the rate of complications. For this reason, it is crucial to select the treatment method based on the results of a standardized Doppler ultrasound examination.

There were no financial conflicts of interest for any of the participants involved in revising the guidelines.