The most common cause of red urine is hematuria. Hematuria can be associated with cystitis or malignancy along with other causes. Other causes of red urine include other sources of heme including myoglobin. Various foods and drugs can also cause red urine. The most common cause of red urine due to food intake is the ingestion of beets. Porphyrins may cause pink or red urine, and the presence of red urine without dysuria, accompanied by abdominal and pelvic pain, raises the question of porphyria.
New England Journal of Medicine - Vol. 358, No. 26, June 26, 2008