Choluria (or bilirubinuria) is a symptom defining an abnormal darkness of the urine, mainly due to a high level of conjugated bilirubin. Choluria is a common symptom of liver diseases, such as hepatitis and cirrhosis. It can be described as dark or brown urine, often referred to as the color of cola. The presence of choluria is a useful symptom to distinguish if somebody presenting with jaundice has liver disease (direct hyperbilirubinaemia) or haemolysis (indirect hyperbilirubinaemia). In the first case, patients have choluria due to excess conjugated ("direct") bilirubin in blood, which is eliminated by the kidneys. Haemolysis, on the other hand, is characterized by unconjugated ("indirect") bilirubin, which is not water-soluble and is bound to albumin, and thus not eliminated in urine.
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Dark urine in the context of Jaundice
Jaundice, also known as icterus, is a yellowish or, less frequently, greenish pigmentation of the skin and sclera due to high bilirubin levels. Jaundice in adults typically indicates the presence of underlying diseases involving abnormal heme metabolism, liver dysfunction, or biliary-tract obstruction. The prevalence of jaundice in adults is rare, while jaundice in babies is common, with an estimated 80% affected during their first week of life. The most commonly associated symptoms of jaundice are itchiness, pale feces, and dark urine.
Normal levels of bilirubin in blood are below 1.0 mg/dl (17 μmol/L), while levels over 2–3 mg/dl (34–51 μmol/L) typically result in jaundice. High blood bilirubin is divided into two types: unconjugated and conjugated bilirubin.