Lots of people really feel slight stinging or cramping if the needle goes in the vein. Tell your healthcare professional if it hurts a great deal. Pain may outcome from the answer leaking with the vein in to the tissue about it. In case you are a Mayo Clinic patient, https://www.sgvascularctr.com/varicose-vein-treatment-in-singapore-from-the-perspective-of-a-vascular-surgeon/