If these valves are weak or damaged, blood can move backward and pool inside the veins, resulting in the veins to extend or twist. Typically, Mayo Clinic will not require a health practitioner referral. Some insurers have to have referrals or may have more needs for specific health care care. https://www.sgvascularctr.com/varicose-vein-treatment-in-singapore-answers-to-your-most-common-questions/