What is conjugated bilirubin?

What is conjugated bilirubin?

Bilirubin is a yellow-coloured metabolite made during the breakdown of heme and is the primary pigment in bile. It develops due to the breakdown of red blood cell haemoglobin (heme degradation). Bilirubin comes in two varieties: conjugated bilirubin and unconjugated bilirubin.

a blood sample can be used to measure direct bilirubin

Conjugated bilirubin: What Is It?

Direct bilirubin is another name for conjugated bilirubin. This form of bilirubin has been combined with glucoronic acid and is expelled through the bile.

Water soluble and non-toxic, conjugated bilirubin is not harmful to the body.

Conjugated bilirubin levels in adults should typically range from 0.0 to 0.3 mg/dL. Conjugated bilirubin can be filtered by the kidneys since it is water-soluble. Conjugated bilirubin is expelled via the bile into the colon, in which it is deconjugated by the mucosal enzyme -glucuronidase and absorbed by the body through enterohepatic circulation prior to being excreted with the stool.

Unconjugated bile is conjugated by adding glucuronic acid to create conjugate bilirubin. Conjugated bilirubin is just not typically found in urine. However, it could be detected in the urine in specific circumstances or disorders. Conjugated bilirubin will give urine a dark brown, cola- or tea-like hue if it is present.

What is the difference between conjugated and unconjugated bilirubin?

The conjugated bilirubin necessitates the enzyme glucuronyl transferase. The liver's capacity to conjugate bilirubin is compromised by a deficiency in this enzyme or by the presence of medications that inhibit glucuronyl transferase. Lab tests can distinguish between unconjugated and indirect bilirubin or conjugated as well as direct bilirubin due to the bilirubin's chemical differences after it has undergone the conjugation process inside the liver.

Direct and indirect bilirubin reactions to certain dyes are described by the phrases "direct" and "indirect." Water-soluble conjugated bilirubin responds immediately when colours are introduced to the blood tests. Before alcohol is introduced into the solution, the non-water soluble, unbound bilirubin somehow doesn't react with the reagents. As a result, this form of bilirubin cannot be directly measured.

What causes high conjugated bilirubin?

Conjugated hyperbilirubinemia results from an increase in the level of conjugated bilirubin. The bilirubin conjugation level increases for a number of reasons. Conjugated hyperbilirubinemia is mostly caused by:

Hepatocellular Injury:

Viral diseases, including hepatitis A, B, and E, can cause liver damage and deep down to liver cells, causing hepatocellular injury.

high levels of total bilirubin may cause damage


Cholestasis is the reduced production of bile (a gastrointestinal fluid) as a result of injury towards the liver cells. Bile builds up and imposes liver damage. Intrahepatic cholestasis is the term used because this condition develops inside the liver.

Metabolic Activity:

Metabolic activity defects can cause high amounts of bilirubin conjugation at any stage of bilirubin synthesis or secretion.

Biliary obstruction:

A blockage in the bile duct, which delivers bile through the liver and gallbladder towards the intestine, is known as a biliary obstruction.

Other causes

Conjugated hyperbilirubinemia has various other causes, some of which are as follows:

  • Certain drugs and poisons

  • Cholelithiasis

  • Hepatitis virus

  • Hepatitis cirrhosis

  • Sepsis

  • Alcohol

  • Immune system diseases

  • A few metabolic illnesses, including Niemann-Pick and Gaucher diseases.

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What Diagnostic Procedures Can Detect Conjugated Hyperbilirubinemia?

If your doctor suspects you have signs or symptoms of liver problems, bile duct obstruction, hemolytic anaemia, or a metabolic issue related to the liver or ill infants who have jaundice, you need to get tested.

The purpose of a physical examination is to look for any yellowish discolouration of both the skin or eyes, any discomfort or pain inside this right upper region just above the abdomen, or any signs of an abdominal mass.

Total and direct serum test:

Total and direct serum bilirubin levels are checked using blood tests to determine whether there are any health issues. If the levels are high in the blood sample, cholestasis or hepatocellular damage may be the cause.

MRI scan:

Using a powerful magnetic field combined high-frequency radio waves, magnetic resonance imaging (MRI) creates a detailed image of the inside organs in our body. In order to identify the disease, this scan offers a more precise depiction of the structure.

a bilirubin blood test may be included in a liver panel to detect liver injury

PTC, or percutaneous transhepatic cholangioscopy:

This method takes pictures of the bile duct using high-frequency radio waves to evaluate for bile duct obstruction.

Complete blood count

The complete blood count can also offer helpful diagnostic hints. A high white blood cell count could be a sign of illness. A low haemoglobin level may indicate hemolytic anaemia. Increased platelet counts indicate inflammation, but thrombocytopenia could signify hypersplenism and portal hypertension.

ERCP, or endoscopic retrograde cholangiopancreatography:

This procedure entails passing a flexible tube with a light and a camera via the mouth and into the upper digestive system. The food pipe, stomach, and duodenum—the first small intestine segment—comprise the upper gastrointestinal tract and are where x-ray images are taken after the dye injection to observe the bile duct. This method is effective for identifying biliary blockage.

Bilirubin in the Urine:

A urine test is used to determine whether bilirubin is present in the urine. It indicates underlying liver problems if the test results are positive.

What happens if conjugated bilirubin is high?

The bilirubin accumulation inside the tissues occurs whenever the direct bilirubin level rises over 30 to 35 mmol/l.

High bilirubin leads to Jaundice:

Jaundice, a disorder that results in the skin, mucous membranes, and sclera turning yellow, is caused by this build-up of bilirubin. An elevated bilirubin conjugation level within the body may indicate liver disease.

Cholestasis or liver damage

Increased bilirubin conjugation indicates cholestasis or hepatic damage, which may call for bile duct surgery and therapeutic endoscopy.

Conjugated hyperbilirubinemia is not a disease in and of itself. Hence the prognosis varies slightly based on the underlying illness conditions that cause prolonged conjugated hyperbilirubinemia bilirubin levels.

Read more: What is the highest bilirubin level?

Management and Treatment of Conjugated bilirubin

The following management tips are provided for a few of the popular potential aetiologies:

Cancer of the pancreas

The primary treatment modalities include surgery, such as the Whipple technique, and chemotherapy.

Malignant Biliary Tract Obstruction:

Endoscopic biliary drainage or stenting may be used to treat hyperbilirubinemia.


Oral bile salts, such as ursodeoxycholic acid 10 mg/kg/day, and ESWL, may be options for patients who are not surgical candidates or who refuse surgery. In spite of the fact that ursodeoxycholic acid causes cholesterol stones to dissolve by lowering biliary production, 50% of individuals who stop taking medicine within five years develop gallstone recurrence. ESWL is inappropriate in pregnancy, coagulopathy, concomitant anticoagulants, choledocholithiasis, biliary pancreatitis, and these conditions. 70% of gallstones that have undergone lithotripsy will return.

Read more: What is a urinary bilirubin test?

Bottom Line:

The human body produces bilirubin on a daily basis. The liver is where most of these degradation processes take place. Conjugated hyperbilirubinemia develops in a number of conditions where there is bile duct obstruction, which causes obstruction of the biliary flow.

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