DefinitionThe methylene blue test is used to determine the type of the blood disorder, methemoglobinemia.How the test is performedThe health care provider wraps a tourniquet or blood pressure cuff around your upper arm. This creates pressure that causes veins below the area to fill with blood.After cleaning the area with a germ killer (antiseptic), the person performing the test will place a needle into your vein, usually near the inside of the elbow or back of the hand. A thin tube, called a catheter, is then placed into the vein. (It may be called an IV, which means intravenous.) While the tube stays in place, the needle and tourniquet are removed.A dark green powder called methylene blue goes through the tube into your vein. The health care provider looks at how the powder turns a subst