Urine Discoloration
With the popularity of social media and its increasing use in medicine, commentary on urine color and health has recently been surfacing. [1] Additionally, numerous internet medical reference pages list various urine colors and their potential etiologies, and a dedicated site even gives an overview of each. [2] Nonetheless, an excellent 2012 review article by Aycock and Kass on abnormal urine color provides a contemporary insight into an issue explored in the same journal by Raymond and Yarger nearly a quarter century prior. [3, 4] This article outlines some of the more common causes of abnormal urine color.
Normal urine color and clarity
The yellow coloration of urine results from urobilin (or urochrome) that is produced as a product of bilirubin degradation. Specifically, urobilinogen metabolized from bile by intestinal bacteria is reabsorbed and oxidized, producing urobilin that is then renally excreted. Normal urine color ranges from light yellow to golden. This normal variance generally fluctuates based on urine output per hydration and fluid intake in the absence of diuretics. That being said, conditions such as diabetes with glucosuria may lead to osmotic diuresis that dilutes urine and increases its volume. Conversely, ingesting pigments contained in various foods and medications, such as those in multivitamins, may cause the urine to appear darker and more concentrated.
Normal urine is clear but may appear hazy if very concentrated in the face of reduced urine output. The presence of white blood cells, or pyuria, as in infection or inflammation, can also give the urine a turbid appearance. The presence of ejaculate in the urine, whether in the first postcoital void or in the presence of retrograde ejaculation secondary to medications, procedures, or neurologic issues, may also lead to cloudy urine. Proteinuria in such instances can also lead to the development of bubbles as the urine is agitated upon reaching water in the commode. This can also happen to some degree with normal urination. However, the consistent presence of a froth or foam in the commode when urinating may indicate pathologic proteinuria.
Abnormal urine
Orange urine
Generally, orange urine discoloration results from medication use. The most common culprits are rifampin and phenazopyridine. Additionally, riboflavin, sulfasalazine, and warfarin (in the absence of hematuria) have also been implicated. An additional cause of benign orange urine discoloration is the overconsumption of carrots, which may also lead to similar changes in skin appearance. Otherwise, any factors that may cause red urine can also produce orange urine, usually depending on hydration status, considering their proximity on the color spectrum.
Red urine
As with the yellow coloration of normal urine, red urine can range in intensity from a pink lemonade color (clear light pink) to that of tomato soup (active thick bleeding) to a deep opaque merlot color (liquefying clot). Hematuria, or blood in the urine, is likely the most common cause of red urine. Directly visualizing erythrocytes via microscopy is the best means of identifying true hematuria, as dipstick testing can produce false-positive results. The presence of heme in the urine also produces red discoloration and generates a positive dipstick reading; however, this should not be considered hematuria in the absence of microscopic confirmation.
The differential diagnoses for gross hematuria are broad and include, but are not limited to, infection, stone disease, malignancy, trauma, fistula, medical renal disease, and contamination (eg, due to menstruation). Gross hematuria warrants a thorough diagnostic evaluation owing to the poor prognosis associated with some of its underlying etiologies.
Red urine discoloration due to hemoglobinuria may present in hemolytic disorders, as in “march hematuria” observed in troops. [5] Likewise, myoglobinuria due to myocyte destruction (eg, caused by rhabdomyolysis after crush injury) can also result in red urine discoloration. [6] Similarly, the disordered heme production in porphyria can result in red urine discoloration that may change to brown or purple with sunlight exposure.
As with the difference between red and orange discoloration, urine color can vary from red to brown with hydration status.
Numerous medications can cause red urine discoloration. Most commonly, rifampin or phenazopyridine is the culprit, with tears and other bodily fluids generally also discolored. Others include chlorpromazine, thioridazine, senna, and laxatives with a phenolphthalein component. A report of hydroxocobalamin producing red urine discoloration after use in cyanide poisoning has also been documented. [7] Both mercury and lead poisoning have also been implicated in red urine discoloration.
Other more benign causes of red urine discoloration are related to the ingestion of certain pigment-containing foods. Consumption of a large amount of beets can result in red urine with no observable erythrocytes on microscopy or heme on dipstick testing. Heavy consumption of rhubarb or carrots can also cause red urine discoloration.
Brown urine
Brown urine discoloration can stem from numerous causes of red urine. Old clot sediment can appear brown when suspended in urine of a certain concentration. Likewise, myoglobinuria and hemoglobinuria often appear brown in color. To this accord, a report of “rust-colored urine” after intense hand drumming has been published. [8] Medical renal disease can also produce brown urine discoloration. One classic example is the “muddy brown urine” observed in acute tubular necrosis.
The commonly used antibiotics nitrofurantoin and metronidazole can lead to brown urine discoloration. Chloroquine and primaquine have also been implicated. Certain laxatives, as noted elsewhere, can also be causative. Additionally, the consumption of fava beans and aloe has been believed to cause urine to turn brown.
A more serious cause of brown urine is liver failure with elevated circulating levels of bilirubin, which may first be evident in jaundice with yellowing of the skin and sclera. A rarely reported but serious cause of brown urine is metastatic melanoma. This can lead to brown or even black urine if melanocytes implant within the urinary tract and slough into the urine and when melanin itself is cleared renally. [9] Like differences between other urine colors, causes of black urine discoloration can also produce brown urine discoloration with differing urine concentrations.
Black urine
As with other urine color changes, black urine discoloration can stem from causes of red or brown urine depending on urine concentration and the intensity of the color change etiology. Other causes of black urine include laxatives derived from senna leaves and cascara bark, as well as sorbitol, the naturally occurring sugar commonly used as an artificial sweetener. Alpha-methyldopa and L-dopa have also been associated with black discoloration of urine.
Poisoning with phenol has been noted to produce black urine, as has copper poisoning. Ingestion of iodine has also been implicated. A skeletal muscle relaxant, methocarbamol, can also lead to black urine discoloration that varies to blue or green with changes in urine concentration. As mentioned above, melanoma can create black urine. Alkaptonuria, a genetic condition, can also result in urine darkening upon air exposure due to the accumulation of byproducts that result from disordered tyrosine processing. As noted above, the disordered hemoglobin production in porphyria can also produce red or brown urine that may appear black after exposure to sunlight.
Purple urine
Purple discoloration is rare. One cause, as with other discolorations, is porphyria when urine is exposed to sunlight. Purple urine bag syndrome has also been associated with purple discoloration of catheter tubing and urine collection bags. This condition stems from bacteria, usually gram-negative species, in the urine that metabolize indole into 2 components and stain the catheter hardware. [10] Otherwise, conditions that cause blue urine discoloration in the presence of red urine discoloration could theoretically have the same outcome.
Blue urine
Iatrogenic causes are likely the most common reason for blue urine discoloration. The intravenous injection of methylene blue or indigo carmine produces blue urine discoloration. Likewise, ingestion of a sufficient amount of methylene blue, whether isolated or as a component of other medications, home remedies, or supplements, can also create blue discoloration. [11] Conditions with disordered tryptophan processing can result in its urinary excretion, with subsequent bacterial metabolism and blue urine discoloration. Generally, frank blue urine discoloration is rare per the presence of urochrome and the high likelihood that the two combined will cause a green urine color.
Green urine
Causes of blue urine discoloration can also produce a green urine hue when combined with the yellow color urochrome produces. Additionally, consumption of foods and supplements that contain green pigmentation can also provide the same effect. [11] Large amounts of asparagus or black licorice have been noted to cause green urine discoloration. Some medications that have been implicated include promethazine, cimetidine, amitriptyline, metoclopramide, and indomethacin. Additionally, drugs that contain phenol can be metabolized in such a manner that green urine discoloration results.
Certain medical conditions can also lead to green urine discoloration. Urinary tract infection with Pseudomonas species has been observed to produce a green hue in urine. Additionally, fistulas into the urinary tract that facilitate the passage of bile into the urine stream permit its green pigment to stain the urine. [12] Metabolic conditions that cause blue urine discoloration, like the other causes mentioned, can also result in urine appearing green.
White urine
White urine, also called albinuria, is most commonly due to sediment. The presence of mineral crystals (eg, from calcium or phosphate precipitation) can lead to a white or snowy-appearing urine. Other causes of white urine include infection, with funguria often resulting in white sediment from the fungus itself or resultant pyuria. Similarly, substantial bacterial infection can result in pyuria that appears white, as can mycobacterial infection, such as that with tuberculosis involving the urinary tract. Lymphatic drainage into the urinary tract, or chyluria, is another source of white urine discoloration. Mucus in the urine can also cause it to appear white in color. Regardless of the cause, the appearance of white urine generally warrants a thorough diagnostic workup.
