Indirect Bilirubin

Bilirubin consists of the primary bile pigment that is obtained through the breakdown of heme part of the red blood cells. Heme is the deep red as well as oxygen carrying non-protein part of the hemoglobin. It is also known as reduced hematin. When the heme is broken down, it travels to the liver and secreted into bile. In the blood, there are normally small amounts of bilirubin that circulate. 

Bilirubin occurs in two forms, which are the conjugated and unconjugated. Indirect bilirubin is the unconjugated form of the substance and it is fat-soluble meaning that it can dissolve in lipids however; the direct or conjugated form is water-soluble. The indirect bilirubin is converted to soluble form in order to be excreted. The unconjugated bilirubin is transported by albumin to the liver. In the liver, it is conjugated or converted and made water-soluble. 

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The terms ‘direct’ and ‘indirect’ are often the reflection of the way in which these forms of bilirubin react to particular dyes. Conjugated bilirubin will react directly when the dyes are added to a blood specimen but the unconjugated or free bilirubin does not react with dyes or reagents unless alcohol is added to the specimen solution of blood, hence the name ‘indirect’. 

What are the normal ranges of indirect bilirubin?

The recommended normal levels for indirect bilirubin also known as unconjugated or pre-hepatic bilirubin is 0.1 to 1.0 mg/dl. Bilirubin is the substance that gives the bile its color, which is bright greenish yellow. Indirect bilirubin is determined by measuring the total or serum bilirubin and then subtracting the direct bilirubin. What is left after subtracting direct bilirubin from total bilirubin gives the value of indirect bilirubin. 

Nearly all bilirubin is excreted as part of the bile salt components. When bile salts are released to the intestine through the bile duct, they are acted by bacteria and form chemical compounds known as urobilinogens. In the intestine, while a large percentage of urobilinogen is excreted in feces, some will be reabsorbed and travel to the liver however, small amounts are excreted in urine. 

The dark color you see in feces comes from the urobilinogen. When there is absence of bilirubin in intestine as a result of obstruction of the bile duct and reduced conversion of bilirubin to urobilinogen, the stool appears clay in color. 

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Causes of increased levels of indirect bilirubin

Increased or elevated levels of indirect form of bilirubin may be caused by increased production of the substance or decreased conjugation. Hyperbilirubinemia is the increased level of bilirubin in body. In newborns, indirect or unconjugated hyperbilirubinemia may occur due to accelerated erythrocyte hemolysis, a condition known as erythroblastosis fetalis. 

When there is absence of glucuronyl transferase, an enzyme that is necessary for the conjugation process to occur, this may result to increased levels of unconjugated hyperbilirubinemia. The presence of drugs, which interfere with the function of enzyme glucuronyl transferase, may impair the ability of the liver to conjugate bilirubin thus leading to increased levels of indirect form of the substance. 

Hepatocellular disease of the liver may also contribute to increased levels of unconjugated bilirubin. Gilbert’s syndrome may also cause increased levels of indirect bilirubin in blood though it may not have serious health implications. 

Abnormal amounts of indirect bilirubin may indicate a disease. If there are concerns about a medical complication, a doctor may request a blood test to examine the bilirubin levels. Conditions like jaundice may cause the levels to elevate. Jaundice is a condition, which causes skin and eyes to turn yellow. 

How bilirubin test is done

When a bilirubin test is being performed, the doctor will request a patient to fast for a couple of hours. The doctor may ask you to fast for four hours before the test is conducted. If you are taking certain medications, you may need to stop taking them temporarily because they can also affect the results of the tests. The doctor may provide specific directions to the patient to follow before the test is done. 

During the test, small blood is drawn and used as the specimen sample. The results can be obtained fast and depending on the results, the doctor may discuss with you on additional tests as well as treatment options in order to tackle the cause of the rising levels of bilirubin in blood. The results may also vary between different laboratories. 

If you appear healthy and the results are unusually high, the doctor may recommend a repeat of the test to rule out and inconsistence. If instructions are not followed by the patient when preparing for the test, they can lead to false readings. It is important to tell your doctor of any medications you may be taking to evaluate if they should be discontinued. 

In addition, if you have allergic reacts to any medication, you also need to let the doctor know about it. If you have had bleeding problems or you have taken blood thinners such as warfrin and aspirin, you also need to tell the doctor. Pregnancy may also determine how the test should be done. 

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