Bilirubin

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Bilirubin is a yellow pigment, one of the main components of bile. It is formed mainly from hemoglobin, that is found within all red blood cells (RBCs). The life span of red blood cells is about 120 days and they are replaced constantly. As a result of the breakdown of old RBCs, heme molecules from the released hemoglobin are converted into bilirubin. This form of bilirubin is called indirect (free or unconjugated) bilirubin.

Indirect bilirubin is transported by blood to the liver with the help of albumin. In the liver it is conjugated with glucuronic acid and becomes direct (bound, conjugated) bilirubin.

In contrast to unconjugated bilirubin, conjugated bilirubin is water soluble and can be excreted from the body. Conjugated bilirubin is mixed with the bile and transferred through the bile ducts into the small intestine, where it is destroyed by bacteria and excreted from the body in the stool. Bilirubin gives stool its brown color.

A comprehensive bilirubin blood test measures the amount of direct and indirect bilirubin in the blood, as well as its total amount – total bilirubin.

Normal bilirubin levels

There are different reference ranges for adults and for infants. Normal values in newborns depend on the age of the baby and whether the baby was premature or full term.

The concentration of bilirubin in blood is measured in μmol/L (SI units) and mg/dL (conventional units). The conversion formula is as follows:

mg/dL x 17.10 = μmol/L

The reference range may vary among laboratories. The approximate normal range of total bilirubin for adults is 0.2-1.2 mg/dl (3,4-21 mmol/L); direct bilirubin – 0.1-0.4 mg/dl (1,7-6,8 mmol/L); indirect bilirubin – 0.2-0.8 mg/dL (3.4-13.0 mmol/L). For newborns the approximate normal ranges are as follows:

  • less than 24 hours = less than 8.0 mg/dL (137 mmol/L)
  • less than 48 hours = less = Less than 12.0 mg/dL (205 mmol/L)
  • 3 to 5 days = less than 15.0 mg/dL (256 mmol/L)
  • 7 days or older = less than 12.0 mg/dL (205 mmol/L)

Elevated bilirubin levels

A high level of bilirubin in the blood is called hyperbilirubinemia. Elevated bilirubin levels can cause jaundice because of which the skin and eyes become yellow.

There are 3 main reasons that cause high bilirubin level. Problems in the body can occur before, during or after the production of bilirubin.

Before reaching the liver (pre-hepatic jaundice)

Some conditions can lead to the elevated bilirubin levels before it gets to the liver. This is called the pre-hepatic phase and can be caused by hemolytic anemia (increased destruction of red blood cells). This causes increased production of indirect bilirubin.

In the liver (intrahepatic jaundice)

If the liver does not work properly, it may not be able to conjugate bilirubin to glucuronic acid to make it soluble with water. This may result in too much bilirubin staying in the liver.

Possible causes include:

  • Viruses, for example, hepatitis A
  • Alcohol abuse
  • Intoxication with drugs
  • Autoimmune diseases

After leaving the liver (post-hepatic jaundice)

Posthepatic (obstructive) jaundice may occur after conjugation of bilirubin within the liver when bile flow is obstructed between the liver and the intestine. Among the causes are gallstones, scar tissue, pancreatitis, inflammation, or tumors.

High bilirubin in newborns

Jaundice is a common and usually harmless condition in newborn babies (also called neonatal jaundice, infant jaundice). More than half of newborns have visible signs of jaundice (yellowed skin and eyes) in the first week after birth and is evident in about 80% of premature babies.

The most common types of jaundice are:

Physiological jaundice is the most common type. This form of jaundice is usually first seen on the second or third day of life and usually disappears on its own in one to two weeks after birth. Healthy babies are born with elevated hemoglobin levels and hemoglobin differs significantly from that in older children and adults. Erythrocytes (red blood cells) with such hemoglobin are destroyed too rapidly, which causes a huge amount of bilirubin to enter the bloodstream. However, the liver is not yet sufficiently developed to filter out all bilirubin, which leads to an excess of bilirubin in the body (hyperbilirubinemia).

Breast milk jaundice. This type of jaundice often begins at the end of the first week of life. Breast milk jaundice is thought to be due to the infant's immature liver and intestines, which results in a slower removal of bilirubin. Usually such jaundice resolves spontaneously after three or four months without the need to stop breastfeeding.

Breastfeeding failure jaundice can occur when a newborn does not receive enough breast milk. This may be due to difficulty in feeding, or insufficient frequency of feeding, or if the mother does not have an adequate milk supply. In this case dehydration and fewer bowel movements for the newborn results in decreased bilirubin excretion from the body.

In most cases, jaundice in newborns does not require any treatment because it is not a threat to the health and disappears on its own. However, 1 out of 20 newborns has a high enough level of bilirubin in the blood and requires treatment.

Pathological jaundice usually occurs within the first 24 hours of life. It involves a higher level of bilirubin and requires treatment to hasten the removal of bilirubin.

Jaundice that manifests before the first 24 hours of life should always be considered pathological until proven otherwise.

Some cases of severe neonatal jaundice may be due to underlying diseases or conditions, such as:

  • liver disease
  • maternal-fetal blood group incompatibility (Rh, ABO)
  • bacterial or viral infections
  • blocked bile duct or bowel
  • an abnormality of the baby's red blood cells
  • an infection in a baby's blood (sepsis)

In rare cases, if a child with a very high level of bilirubin is not treated, an increased amount of bilirubin in the body may have a toxic effect on brain and nerve cells.

Symptoms of highly elevated bilirubin levels include poor sucking or feeding, shrill cry, listlessness or difficulty waking, backward arching of the neck and body.


Comprehensive Metabolic Panel (CMP) Interpretation