What is bilirubin?
Bilirubin is a molecule formed by the breakdown of red blood cells and other cells with porphyrins. Red blood cells carry special molecules, called hemes (a type of porphyrin), that house an iron atom. This arrangement allows red blood cells to carry oxygen. When blood cells break down, they release heme into the blood, which could cause damage if left unchecked.
Heme is actively broken down in the liver, as seen in the image below. It first becomes biliverden. Another enzyme continues the process and converts biliverden to bilirubin.
Then, the bilirubin is deposited in the intestines, through the bile duct. From there it can be excreted in urine or feces. In the intestines, it turns into stercobilin, a reddish-brown substance that gives stool its distinctive color. In urine, bilirubin turns into urobilin, a very yellow substance.
Bilirubin, because it is related to porphyrin molecules, is a natural pigment. As it changes to different molecules and versions, it also changes color. Scientists can use these colors to detect disease.
For example, a hematoma is caused by a pool of blood under the skin. The accumulated blood is dark red or purple in color, and will slowly turn more brown as the iron oxidizes.
As blood is drawn and recycled, the heme groups must break down. Heme first turns into biliverden, which has a greenish tint. If you’ve ever had a large bruise that looked greenish, this is why. After this, it turns into bilirubin and has a distinctive yellow color. Old bruises will turn this distinctive yellow before disappearing.
The distinctive yellow coloration of bilirubin accumulation is a common symptom of conditions such as jaundice, in which bilirubin accumulates throughout the body.
This can happen in babies, when the liver has not yet fully developed, or in adults with non-functioning livers. While the yellowing of the eyes and skin is a definite sign that something is drastically wrong, a bilirubin test can show bilirubin levels long before they become dangerous.
Bilirubin is also found in plants as a product of the breakdown of chlorophyll, a molecule closely related to the heme molecules of animal cells. It is also very similar to the pigment phycobilin, which is used by autotrophic bacteria to capture energy from sunlight.
Conjugated versus Unconjugated Bilirubin
Bilirubin exists in multiple forms in your blood. It exists in a water-soluble form, which binds to glucuronic acid in the liver by a special enzyme. This makes bilirubin easier to detect and is known as conjugated bilirubin. Unconjugated bilirubin, on the other hand, is fat-soluble, making it harder to detect in solution. As such, some of this bilirubin is undetectable. It sticks to itself and other fat-loving molecules.
Therefore, a test of a person’s total bilirubin includes direct measurement of soluble bilirubin, plus estimated indirect bilirubin. These two forms, and their abundance in the system, can tell the doctor a lot about which process can be disrupted in the liver.
For example, a healthy person will have a higher concentration of unconjugated bilirubin, but the exact levels depend on the person and the circumstances.
Normal levels of total bilirubin can range from 0.1 to 1.2 milligrams per deciliter of blood, and direct bilirubin will only be 0.1 to 0.4 mg / dL of that. Hyperbilirubinemia conditions, or a really high bilirubin level, can occur for many reasons.
Total blood bilirubin would have to be much higher than this before this condition began to appear. Usually, around 10 mg / dL of symptoms of bilirubin build-up can be seen, such as jaundice of the eyes and skin. This is around 10 times the normal levels.
It could be caused by a rapid loss of blood cells, a non-functioning liver, or a variety of other conditions that prevent the liver or other organs from properly processing bilirubin.
This condition could also be caused by a bile duct blockage, hepatitis, or certain pharmaceuticals that interfere with the passage or conversion of bilirubin. Your doctor will have many other tests to consider, as your bilirubin levels can indicate many different conditions.
Urine Bilirubin Test
Healthy people do not normally excrete bilirubin in the urine. It normally becomes another chemical, which is much more soluble in water.
Bilirubin in the urine is a symptom of a number of the liver, kidney, and intestinal diseases in which a biological process is obstructed. Finding bilirubin in the urine can help a doctor differentiate in which excretory system the error is occurring.
There are many factors that will help determine this, including the type of bilirubin found and its amount.
What is bilirubin? Bilirubin Test, And Urine Bilirubin Test