Serum Bilirubin Test – Normal Values

Most of the bilirubin is produced when there is degradation of hemoglobin during the normal process of removing old or aged cells. The natural color of this substance is yellow. Through the digestive agent known as bile, the bilirubin is transmitted out of your body. It may also be excreted through urine. The color of bile is derived from this substance. In addition, the yellow color of urine also comes from bilirubin. Serum bilirubin is the amount of bilirubin in blood. 

Bilirubin is secreted in intestine together with bile salts and sodium where the bile salts form micelles that facilitate the absorption of fats. Bilirubin occurs in two forms, the conjugated and unconjugated. When in intestine, bilirubin is conjugated (turned into water-soluble substance) by enzymes of bacteria further degrading to urobilinogen. 

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Some of the urobilinogen is re-absorbed back and take up by the liver where it is secreted in the bile again. However, the larger amount of the urobilinogen is broken down into urobilin and stercobilin and then excreted in feces. Naturally, small amounts of bilirubin circulate in blood however, when there is elevated level of this substance, it may indicate problems within the liver.

The amount of conjugated bilirubin that is presence in serum is healthy if it is in small amounts. However, when the level of conjugated serum bilirubin is high, it implies a disease. Only conjugated bilirubin is found in urine, if a person has bilirubinuria, it also indicates a liver disease. Bilirubinuria is an abnormality where conjugated bilirubin is detected in urine. 

Moreover, unconjugated bilirubin bounds tightly to albumin and it is not filtered by the glomerulus of the kidney and therefore, it is absent from urine even when there is increased levels of unconjugated bilirubin. When urine tests positive for bilirubin, it only confirms that there is increased conjugated hyperbilirubinaemia. 

When the reticuloendothelial system breaks down red blood cells and unconjugated bilirubin is taken to the liver by albumin, this is known as pre-hepatic bilirubin. The normal range for unconjugated is 0.1 to 1.0 mg/dl. In the liver, unconjugated bilirubin is converted to water soluble, and this is called post-hepatic or conjugated bilirubin. The normal values for conjugated bilirubin are 0.0 to 0.4 mg/dl. 

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Tests for serum bilirubin levels can assist in giving accurate assumption on the function of liver. In a health person, bilirubin is taken up by the liver and sent to the bile. If there is failure or drop in function of liver, it means that less of bilirubin is taken up and it may remain in blood something that raises the levels. Moreover, the function of the liver in conjugating or making the bilirubin water-soluble may be impaired by other factors like drug abuse. 

Side effects of medications may also change the way in which the liver conjugates bilirubin. Elevated levels of serum bilirubin indicate effect of drugs on liver function like antibiotics, steroids, barbiturates, and oral contraceptives. In chronic acquired liver diseases, the levels of serum bilirubin concentration may remain normal until that time the liver receives a considerable damage or cirrhosis develops. In acute liver disease, the level of serum bilirubin normally increases in relation to the severity of the disease. 

For this substance to be conjugated, the presence of an enzyme known as glucuronyl transferase is required. A person with elevated levels of bilirubin may lack this enzyme. Glucuronyl transferase is utilized by liver in processing bilirubin or changing it into water-soluble form and if this enzyme lacks, it means that high levels of bilirubin are found in blood. 

High levels of serum bilirubin are associated with jaundice. Abnormal levels of bilirubin cause discoloration of body tissues. If the levels are more than 3milligrams per deciliter, jaundice is likely to occur. A person with jaundice has yellow sclera, the white part of eye. In addition, a person with jaundice may also have yellow skin in the entire body. Other symptoms of jaundice include nausea, fever, body ache, lack of appetite, inability to pass motion regulation, and extreme fatigue. 

The presence of jaundice may necessitate the doctor to determine whether the increased levels were as a result of post-hepatic or pre-hepatic jaundice. If there is increased unconjugated bilirubin, it indicates pre-hepatic or hepatic jaundice and it can be treated medically. However, when there is increased conjugated bilirubin, it indicates post-hepatic jaundice and this condition may require surgery of the bile duct or a therapeutic endoscopy. 

Physiologic jaundice occurs in newborn due to immature liver that lacks sufficient conjugating enzymes. If the newborn’s liver cannot conjugate bilirubin, this situation results to high levels of this substance circulating in blood. If these high levels of unconjugated bilirubin are not treated, they can pass through the blood-brain barrier causing brain damage. Therefore, the levels should be monitored to prevent such complications. The baby may be exposed to ultraviolet rays to try decreasing the levels. 

Gilbert’s syndrome is a harmless genetic condition in which people experience occasional jaundice. Gilbert syndrome produces increased levels of unconjugated bilirubin in blood but it has no serious implications. 

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