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General Practice 2023

Direct and indirect bilirubin: what é and why can it be high

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Direct and indirect bilirubin: what é and why can it be high
Direct and indirect bilirubin: what é and why can it be high

The bilirubin test helps in the diagnosis of liver problems, bile ducts or hemolytic anemia, for example, since bilirubin is a product of the destruction of red blood cells and to be eliminated by the body it needs to be conjugated to a sugar in the liver and suffer the action of bile.

There are two main types of bilirubin that can be measured with this test:

  • Indirect bilirubin or unconjugated: is the substance that is formed when red blood cells are destroyed in the blood and then transported to the liver. Therefore, its concentration is higher in the blood and may be altered when there is a condition involving red blood cells, such as hemolytic anemia, for example;
  • Direct bilirubin or conjugated: corresponds to the conjugation between bilirubin and glucuronic acid, a sugar, in the liver. Direct bilirubin undergoes the action of bile in the intestine, being eliminated in the form of urobilinogen or stercobilinogen. Thus, the concentration of direct bilirubin is altered when there is liver damage or biliary obstruction.

A bilirubin test is ordered to assess liver function, monitor the treatment of jaundiced newborns, and assess diseases that may interfere with bilirubin production, storage, metabolism, or excretion. Normally the doctor requests the total bilirubin, however the laboratories also usually release the direct and indirect bilirubin dosages, since these two dosages are responsible for the total bilirubin value. See what other tests help to identify liver problems.

The bilirubin test requires no preparation and is performed with a small amount of blood. However, the result of this test may suffer interference when the sample is hemolyzed, that is, when the amount of red blood cells destroyed is very large, which usually happens when the collection is not performed correctly. That's why it's important that the collection is done in a reliable laboratory and with trained professionals.


Bilirubin reference values

The blood bilirubin reference values are:

Type of bilirubin Normal value
Direct Bilirubin up to 0.3 mg/dL
Indirect Bilirubin up to 0.8 mg/dL
Total bilirubin up to 1.2 mg/dL

Some newborns may have very high bilirubin levels, which may be due to immaturity of organs related to bilirubin metabolism or the stress of childbirth. The reference values for bilirubin in babies vary according to their life span, being:

  • Up to 24 hours after birth: 1.4 - 8.7 mg/dL;
  • Up to 48 hours after birth: 3.4 - 11.5 mg/dL;
  • Between 3 and 5 days after birth: 1.5 - 12 mg/dL.

After the 6th day the reference values are the same as those of the adult. Values above the reference value indicate that the baby has jaundice, which is one of the most frequent diseases in newborns and can be easily treated through phototherapy, which aims to reduce the concentration of bilirubin in the baby's body. Learn more about neonatal jaundice, causes and treatment.

When to take the bilirubin test

The bilirubin test is usually ordered by the doctor when there are symptoms of liver problems, such as excessive tiredness, frequent nausea, vomiting, constant pain in the belly, dark urine or yellow skin, for example.

However, this test can also be used when cirrhosis, hepatitis and hemolytic anemia is suspected, for example, which causes signs such as pallor, frequent sleep, dry skin, hair loss or weak nails. See other symptoms of hemolytic anemia.

Decreased bilirubin levels are usually due to the use of certain medications, however, elevated bilirubin levels usually indicate he alth problems that can be serious if left untreated.


What can high bilirubin be

The cause of increased bilirubin in the blood varies depending on the type of bilirubin that is increased:

Indirect bilirubin increase

In these cases, the change in bilirubin levels is almost always caused by a change in the blood, however, the main causes include:

  • Hemolytic anemia;
  • Pernicious anemia;
  • Hemoglobinopathies;
  • Blood transfusions.

In addition, there are also cases where indirect bilirubin is increased due to a syndrome, known as Gilbert Syndrome, in which there is a genetic change that prevents the liver from properly eliminating bilirubin. Learn more about Gilbert Syndrome.

Increased direct bilirubin

When there is an increase in direct bilirubin it is usually a sign that there is a problem with the liver or bile ducts. Thus, some of the main causes include:

  • Viral hepatitis;
  • Alcoholic liver disease;
  • Stone in the bile ducts;
  • Tumors in the liver or bile ducts.

Overuse of drugs that affect the liver, such as Paracetamol, can also lead to an increase in this type of bilirubin in the blood. Understand better about what causes increased bilirubin and jaundice in adults.

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