X-Ray - Intravenous Contrast Media

Some tests require an injection into a vein in the arm. The liquid injected is called x-ray contrast or "dye", a misnomer, as the liquid is colourless and cannot stain anything! The term "dye" is used as an analogy to help with the understanding of the way it works.

The contrast contains tiny dissolved molecules which contain the element Iodine. You may know Iodine as a brown liquid used as an antiseptic (eg Betadine). The x-ray contrast is colourless as there is no freely dissolved Iodine in the liquid. All the Iodine is attached to a molecule which was specifically designed to be absorbed by the kidneys, and so pass out of the body within urine. It will not colour the urine.