Bilirubin (clinical analyzes)




Bilirubin is a reddish-yellow substance (hence the name) and is the main component of bile (liquid, produced by the liver and accumulated in the gallbladder, which intervenes in the digestive processes).

The production of bilirubin is mainly linked (80%) to the process of destruction of a protein, hemoglobin, present inside the red blood cells with the function of transporting oxygen to all the tissues of the body, or to the degradation of other proteins.

The first step in its disposal is done in the spleen, where bilirubin is produced and then released into the bile. In this phase the bilirubin is defined live (or not conjugated), because it is not yet soluble in water and does not have the characteristics suitable for being eliminated through the faeces. Therefore, it must bind to another protein in the blood, albumin, to be transported to the liver. Once in the liver, bilirubin is conjugated with two molecules of another substance, glucuronic acid, thus becoming soluble and thus making it possible to excrete it in the bile.

Due to its bond with glucuronic acid, bilirubin is defined direct (or conjugated).

The bilirubin values ​​in the blood tend to rise when there are problems with the spleen, liver or if there are obstructions (for example stones) in the gallbladder that prevent it from emptying the bile or if the process of destruction of red blood cells occurs too fast.

The test

The test

Bilirubin is measured by taking a small amount of blood, through a needle inserted into a vein in the arm, and analyzing it. In infants, blood is drawn from the heel. Fasting before performing the test is not necessary but, often, it is still required in analysis laboratories.

The test result delivered by the analysis laboratory provides the values ​​of the total bilirubin, of that direct and of that live.

The examination (test) can be prescribed as part of a normal check (routine check) but is required, above all, in the case of:

  • presence of jaundice (the obvious sign of which is the yellowish color of the skin and the whites of the eyes)
  • alcoholism
  • suspected drug toxicity
  • suspicion of hepatitis or other forms of liver damage

The test is also useful for:

  • monitor the progression of particular liver diseases, such as hepatitis
  • evaluate the toxicity of a drug
  • understand if the bile ducts are blocked, for example, from gallbladder stones
  • evaluate for possible haemolytic anemia

To get a complete picture of liver function it is often prescribed in combination with other laboratory tests such as alkaline phosphatase, and transaminases (aspartate aminotransferase and alanine aminotransferase).

In case of suspected anemia, it is prescribed together with other tests such as blood count, reticulocyte count, haptoglobin and lactate dehydrogenase (LDH).

Bilirubin is normally excreted through the faeces; a minimal amount is reabsorbed by the blood and, through the liver, eliminated with the bile. A small amount escapes the liver filter and, therefore, a minimal dose is also excreted through the urine. If the quantity of bilirubin is to be measurable in the urine, there is usually a "blockage of the hepatic or biliary ducts, a" hepatitis or other forms of liver damage and can be determined at the onset of the disease; for this reason bilirubin is also measured in the urinalysis.



Normally the total quantity of bilirubin present in the blood (given, therefore, by the sum of that free and of that conjugated) is between 0.3 and 1.0 milligrams per deciliter (mg / dl) of blood.

The reference value of the direct bilirubin (or conjugated) is between 0.1 and 0.3 mg / dl.

The value of the indirect bilirubin, instead, it is obtained by subtracting the direct bilirubin from that total and should normally be between 0.2 and 0.8 mg / dl.

The reference values ​​may change from one laboratory to another, therefore it is essential to refer to normal values ​​(range) reported on the results sheet and contact the attending physician, who knows the health of his patients, to have them evaluated.

If there are high values ​​of total bilirubin, it is important to check whether this is due to an increase in that live or that direct. The rise of the indirect bilirubin (or not conjugated) can be the result of:

  • haemolytic anemias
  • mononucleosis
  • sickle cell anemia
  • acute or late haemolytic reactions (induced, for example, by drugs or as a result of transfusion)
  • hepatitis e cirrosthe
  • fetal erythroblastosis
  • Gilbert's syndrome, a fairly common inherited syndrome due to low levels of the enzyme that produces direct bilirubin

If the direct bilirubin (conjugated) is higher than that live (not conjugated), it means that the liver cells are unable to eliminate bilirubin well. The most common diseases that can cause this problem are:

  • viral hepatitis
  • alcoholic hepatitis
  • drug reaction
  • obstruction of the bile ducts due to stones or injury to the bile ducts or tumor

Finally, the increase in bilirubin may be due to rare hereditary diseases that cause abnormalities in its metabolism (Rotor, Dubin-Johnson, Crigler-Najjar syndromes).

If the bilirubin value is low, the anomaly is not important.

In newborns, the level of bilirubin is measured as a routine check: even if it is elevated, it is normally physiological and resolves in a few days (maximum two weeks).

Blood tests and, therefore, the detection of the bilirubin concentration can be influenced by particular factors: for example, bilirubin values ​​are generally lower in women and children; even physical exertion and the intake of some drugs can affect their values. It is therefore advisable to report any pharmacological therapies in progress to the doctor.



Niguarda Hospital. Total and fractionated bilirubin

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