Blue and Green Urine

Blue urine most typically appears to be caused by ingestion of methylene blue.[43,44] This substance is used in the United States for diagnostic tests, treatment of methemoglobinemia,[45,46] or as a treatment for refractory hypotension.[47] Outside the country, however, oral methylene blue may be found in medications and home remedies because it has antimicrobial properties.[48,49] True blue urine seems to be exceedingly rare, possibly because blue pigments combine with urochrome, the major contributor to urine's normal yellow hue, to create a green color before urine's elimination. In that regard, there are many case reports in which methylene blue turns urine green.[50–52]

Other medications associated with green urine may contain phenol groups and include promethazine,[52] thymol,[53] cimetidine,[54] and propofol.[55–58] The mechanism of action appears to be caused by phenol's conjugation by the liver and subsequent excretion by the kidneys.[59,60] The strength of the green seems to be dose related.[58] Curiously, propofol also is associated with pink[61] and white urine.[62]

Some nonphenol drugs noted to produce green urine are metoclopramide,[63] amitriptyline,[64] and indomethacin. In any event, the urinary findings of all of the above medications are benign effects and do not acquire further workup once urinalysis results are normal.

There are isolated case reports of parenteral absorption of tetrahydronaphthalene (Cuprex),[65] a pesticide that was used in the 1980s as an over-the-counter treatment for lice, and ingestions of the herbicides mefenaceta and imazosulfuro producing green urine.[66] A patient who has come in contact with these compounds should be treated as if he or she were poisoned and deserves full toxicology workup, stabilization, and possible admission to the intensive care unit.

In the critical care setting, patients receiving enteral tube feeds have on occasion been noted to produce green urine. The belief is that the food coloring additive Food Dye and Color Blue Number 1 (FD&C Blue No. 1) is absorbed from the gastrointestinal (GI) tract in high enough concentrations to cause dark green urine.[67,68] In animal models, >1% of FD&C Blue No. 1 is found in rat urine.[69] This finding is harmless and disappears with changes in tube feeds.

Not all causes of green urine are innocuous, however. Pseudomonas-causing bacteremia and urinary tract infections can present with green urine.[60,64] In this case, the patient's history and physical examination should point to an infectious disorder and urine and blood cultures may make the diagnosis. Treatment is centered on clearing the infection rather than on urine color.

Bile pigments in the urine represent a rare but worrisome cause of discoloration. Upon discovering biliverdin, clinicians must take a careful and thorough history to determine the location of the leak. Radiographs or invasive imaging may even be required. A case report of an enterovesical fistula caused by pelvic radiation therapy provides one such source of bile.[70] Other rarer causes of blue and green urine include conditions that impair amino acid absorption from the GI tract.

Blue diaper syndrome[71] and Hartnup disease[60] are autosomal recessive disorders in which tryptophan builds up in the GI tract, causing bacteria to metabolize it to indole, leading to a buildup of indican in the urine. The blue coloring by itself is not dangerous, but it does point to another underlying condition that requires investigation.