If there is a family history of DVT (deep vein thrombosis), blood tests may be ordered to exclude a familial blood clotting disorder prior to treatment (over 5% of the population have some inherited or acquired blood clotting disorder). Sometimes there is significant backflow from the deep to the superficial leg veins. This occurs from incompetent or leaking valves in the veins. In some cases our doctors will order a doppler ultrasound examination of your legs to clarify if this is present, as other therapy such as vein stripping or endovenous laser treatment may be needed to achieve good results. Some conditions are a contra-indication to sclerotherapy. A previous DVT is an important contra-indication, as are a medical history of auto-immune disease or significant other illness.