Bilirubin: Definition, Test, Levels in Urine

Bilirubin Definition

Bilirubin is a yellowish or reddish-orange pigment that is formed when red blood cells are broken down. It is part of the bile, which is made in the liver and stored in the gallbladder. Bilirubin can be measured through a blood test. The term “bilirubin” comes from the Latin word for “red bile”.

What is Bilirubin?

Bilirubin is a yellow-orange pigment that is formed when red blood cells are broken down. It is part of the bile, which is made in the liver and stored in the gallbladder[1]. Bilirubin is mainly formed by hemoglobin breakdown at the end of red cell life, and most of it leaves the body in feces.

There are two types of bilirubin in the blood: water-insoluble or unconjugated bilirubin, which refers to the pigment before it reaches the liver, and water-soluble or conjugated bilirubin, which is excreted into bile after being converted in the liver.

Blood tests for total bilirubin measure both unconjugated and conjugated bilirubin and are performed to evaluate jaundice, anemia, and various liver diseases.

Under normal circumstances, only a very small amount of urobilinogen (a product of bilirubin metabolism) is excreted in the urine. If liver function is impaired or biliary drainage is blocked, some of the conjugated bilirubin leaks out of hepatocytes (liver cells) and appears in the urine, turning it dark amber.

Bilirubin has a half-life of 2 to 4 hours when free-of-bound but has a half-life equivalent to that of albumin since delta bilirubin (a type of conjugated bilirubin) binds to albumin. The half-life yields 2-3 weeks.

Bilirubin Test

A bilirubin test is a medical test that measures the levels of bilirubin in the blood. Bilirubin is a yellowish pigment that is produced during the normal process of breaking down red blood cells. It passes through the liver and is eventually excreted out of the body.

The test can help find the cause of health conditions like jaundice, and it can measure both direct and indirect bilirubin levels. High bilirubin levels may indicate liver disease or other medical conditions.

Conjugated versus Unconjugated Bilirubin

Bilirubin is a yellow-colored pigment and a metabolite of heme. It is formed when the hemoglobin of red blood cells undergoes breakdown (heme degradation). There are two types of bilirubin: conjugated and unconjugated bilirubin. Unconjugated bilirubin is insoluble in water, whereas conjugated bilirubin is soluble in water.

Conjugation alters the physicochemical properties of bilirubin, making it water-soluble, which allows it to be transported in bile without a protein carrier. Conjugation also increases the size of the molecule.

Unconjugated bilirubin requires the protein albumin for transport to the liver, where it undergoes conjugation by adding glucuronic acid. Conjugation makes bilirubin water-soluble and non-toxic for the human body.

Conjugated bilirubin is present in bile, while unconjugated bilirubin is not present in bile. Normally, conjugated bilirubin is not present in urine; however, in certain conditions or diseases, it may be seen in urine giving it a dark cola or tea-like color (brown).

Elevations in total serum bilirubin levels can occur due to various reasons such as liver failure or malfunctioning of liver cells. If unconjugated bilirubin levels are higher than conjugated bilirubin levels, this could be caused by hemolytic or pernicious anemia, transfusion reactions, and cirrhosis.

 If conjugated bilirubin levels are higher than unconjugated bilirubin levels, this is typically due to drug reactions, hepatitis, as well as any type of liver disease.

Urine Bilirubin Test

A bilirubin in urine test measures the levels of bilirubin in your urine. Normally, urine doesn’t have any bilirubin. If there is bilirubin in your urine, it may be an early sign of a liver condition. Bilirubin is a yellow substance that your body makes during the normal process of breaking down red blood cells.

Bilirubin is a yellowish pigment found in bile, which is a fluid produced by the liver and stored in the gallbladder. A lab test can measure the amount of bilirubin in the urine. Large amounts of bilirubin in the body can lead to jaundice. High levels of bilirubin may indicate liver or biliary disease.

Testing bilirubin levels through urinalysis is painless but requires attention to detail and a time commitment. To prepare for a bilirubin urine test, visit your local medical testing lab to get the special container needed to collect your urine.

On the day you begin the test, don’t collect urine the first time you urinate because it’s usually more concentrated. After that, start collecting your urine each time you urinate throughout the day. In healthy people, bilirubin doesn’t appear in their urine.

Bilirubin levels are affected by age and overall health. For babies, high levels of bilirubin can lead to neurological damage. This is why it’s important to check their bilirubin levels.

High bilirubin levels in Urine

A bilirubin urine test measures the amount of bilirubin in the urine. High levels of bilirubin in the urine may indicate liver or biliary disease. Bilirubin can break down in light, which is why babies with jaundice are sometimes placed under blue fluorescent lamps.

High levels of bilirubin in the blood can cause jaundice, a yellow cast to the skin, and whites of the eyes. Other symptoms include nausea, vomiting, lack of appetite, fatigue, weakness, itching, pale stools, dark urine, unexplained weight loss, and fever.

High bilirubin levels may be due to biliary tract disease, cirrhosis, gallstones in the biliary tract, hepatitis, or tumors of the liver or gallbladder.

If someone has high bilirubin levels in their urine or blood, they should follow up with a doctor to determine if there is an underlying condition that needs treatment. Treatment for high bilirubin levels depends on the underlying cause.