Bilirubin is a dark yellow waste product that is primarily created when the body breaks down hemoglobin, which is the protein in red blood cells that carries oxygen. Bilirubin is found in bile, which is fluid in your liver that is involved in digesting food. Most bilirubin is eliminated in the feces or urine. The bilirubin test checks the health of your liver by measuring the amount of bilirubin in blood or in your urine. This can help diagnose or monitor problems related to your liver or red blood cells when the bilirubin level is too high.