Summary

Conjugated bilirubin, a component of total bilirubin, is a type of bilirubin processed by the liver for excretion. Elevated levels of conjugated bilirubin can indicate issues with the liver's ability to excrete bilirubin or problems with bile flow. Conditions like cirrhosis, hepatitis, or bile duct obstruction could cause such elevations, while typically, low levels are not clinically significant.

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Overview

Conjugated bilirubin, also known as direct bilirubin, is bilirubin metabolized by the liver to be excreted into the bile. It can also be referred to as direct bilirubin because it can be measured directly. On the other hand, unconjugated  (indirect) bilirubin is calculated by subtracting the value of conjugated bilirubin from total bilirubin. 

High levels of conjugated bilirubin, a form of hyperbilirubinemia, can indicate a problem with the liver's ability to secrete bilirubin into the bile or an obstruction in the bile ducts preventing the flow of bile into the digestive system. This could be due to conditions such as liver cirrhosis, hepatitis, or a blockage in the bile ducts. Elevated conjugated bilirubin often leads to symptoms like jaundice (a yellowing of the skin and eyes), dark urine, and light-colored stools. On the other hand, low levels of conjugated bilirubin are generally not a cause for concern and can occur due to normal physiological variations or under the effect of certain medications.^[1,2]

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What should you know about this biomarker?

Each laboratory uses different machines and protocols, so the results might vary in terms of the reference ranges or used units of measurement. In Macromo blood tests, we use µmol/l (micromol per liter).

Optimal levels of conjugated bilirubin typically range from 1.5 to 5 µmol/l. High levels can suggest liver disease, biliary obstruction, or other conditions that affect the liver's ability to expel bilirubin. Low levels are not usually a cause for concern and may be seen in healthy individuals.^[3]

Your blood test can show distinct result possibilities:

• The levels of conjugated bilirubin are low, which is generally not a cause for concern. 
• The levels of conjugated bilirubin are within the reference range, which is the desired result.
• The levels of conjugated bilirubin are above the reference range. While this isn't a cause for immediate alarm, contact your healthcare provider, also in case you notice any yellowing of the skin or eyes. 

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Genetics

Genetics can impact conjugated bilirubin levels in the blood. Certain genetic disorders can result in abnormally high or low levels of this compound, leading to a range of potential health issues.

Gilbert's Syndrome is a condition that typically affects levels of unconjugated or indirect bilirubin. It's a common genetic disorder that affects bilirubin metabolism. People with Gilbert's Syndrome have a reduced level of an enzyme called uridine diphosphate glucuronosyltransferase (UGT1A1). This enzyme is responsible for converting unconjugated bilirubin into the conjugated form.^[4,5] 

In Dubin-Johnson Syndrome, there is a mutation in the ABCC2 gene, which reduces the liver's ability to secrete conjugated bilirubin into bile. As a result, conjugated bilirubin builds up in the liver and spills over into the blood. Rotor syndrome also presents with increased conjugated bilirubin, but the exact genetic cause is a bit more complex, involving mutations in both the SLCO1B1 and SLCO1B3 genes.^[6]

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Recommendations

When conjugated bilirubin levels fall outside the normal range, it's important to consider the following recommendations^[7]:

• To rule out genetic conditions like Dubin-Johnson Syndrome, Rotor Syndrome, or others, genetic testing may be advised.
• Depending on the test results, you might be referred to a gastroenterologist or hepatologist specializing in liver diseases.
• A balanced diet rich in fruits, vegetables, lean proteins, and whole grains can support liver health.
• Staying properly hydrated helps maintain optimal bodily function, including the liver and digestive processes.
• Excessive alcohol consumption can cause liver damage and affect its ability to function properly, including its capacity to process and excrete bilirubin. Reducing or eliminating alcohol intake can be beneficial.
• Regular physical activity can improve overall health and help maintain a healthy weight, supporting liver function.
• Smoking can lead to liver damage and various other health issues. If you smoke, quitting will likely improve your health.

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The information and tests provided on our website are for educational purposes only and are not a substitute for professional medical advice. Always consult with your healthcare provider before making health decisions. Our tests do not diagnose or treat diseases. Individual results may vary and should be discussed with a healthcare provider.