Diagnosis
History and examination by a clinician for characteristic signs and symptoms are sufficient in many cases in ruling out systemic causes of venous hypertension such as hypervolemia and heart failure. A duplex ultrasound (doppler ultrasonography and b-mode) can detect venous obstruction or valvular incompetence as the cause, and is used for planning venous ablation procedures, but it is not necessary in suspected venous insufficiency where surgical intervention is not indicated.Insufficiency within a venous segment is defined as reflux of more than 0.5 seconds with distal compression. Invasive venography can be used in patients who may require surgery or have suspicion of venous stenosis. Other modalities that may be employed are: ankle-brachial index to exclude arterial pathology, air or photoplethysmography, intravascular ultrasound, and ambulatory venous pressures, which provides a global assessment of venous competence. Venous plethysmography can assess for reflux and muscle pump dysfunction but the test is laborious and rarely done.The venous filling time after the patient is asked to stand up from a seated position also is used to assess for CVI. Rapid filling of the legs less than 20 seconds is abnormal. Classification
CEAP classification is based on Clinical, Etiological (causal), Anatomical, and Pathophysiological factors. According to Widmer Classification for assessment of chronic venous insufficiency (CVI), diagnosis of chronic venous insufficiency is clearly differentiated from varicose veins.
It represents late sequelae of lipodermatosclerosis where the skin has lost its nutrient blood flow. Lipodermatosclerosis,  an indurated plaque in the medial malleolus. Malignancy, malignant degeneration being a rare but important complication of venous disease since tumors that develop in the setting of an ulcer tend to be more aggressive. Pain, a feature of venous disease often overlooked and commonly undertreated. Anxiety
Depression
Inflammation
Cellulitis

Causes
The most common cause of chronic venous insufficiency is reflux of the venous valves of superficial veins. This may in turn be caused by several conditions:

Deep vein thrombosis (DVT), that is, blood clots in the deep veins. Chronic venous insufficiency caused by DVT may be described as postthrombotic syndrome. DVT triggers an inflammatory response subsequently injuring the vein wall. Superficial vein thrombosis. Phlebitis
May–Thurner syndrome. This is a rare condition in which blood clots occur in the iliofemoral vein due to compression of the blood vessels in the leg. The specific problem is compression of the left common iliac vein by the overlying right common iliac artery. Many May-Thurner compressions are overlooked when there is no blood clot. More and more of them get nowadays diagnosed and treated (by stenting) due to advanced imaging techniques.Deep and superficial vein thrombosis may in turn be caused by thrombophilia, which is an increased propensity of forming blood clots.Arteriovenous fistula (an abnormal connection or passageway between an artery and a vein) may cause chronic venous insufficiency even with working vein valves.