The measurement of direct bilirubin in serum is used to evaluate liver function and the occurrence of jaundice.
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Bilirubin, a bile component, is formed in the liver, spleen, and bone marrow. It is also formed due to the breakdown of hemoglobin, such as during the destruction of red blood cells. There are three types of bilirubin: total, direct (conjugated), and indirect (unconjugated). Total bilirubin is the sum of direct bilirubin plus indirect bilirubin. The level of total bilirubin is increased in any jaundice.
Direct or conjugated bilirubin is typically excreted from the gastrointestinal tract, with only small amounts entering the bloodstream. It was initially called “direct” because this water-soluble bilirubin reacts directly with the reagent added to the samples. Its level increases in the blood during obstructive jaundice (from gallstones), and jaundice occurs because the bilirubin cannot reach the intestine to be excreted and instead enters the bloodstream to be excreted by the kidneys. Direct bilirubin is the only type of bilirubin that can cross the renal glomerulus and is thus the only type of bilirubin found in the urine.
Indirect bilirubin, also known as free or unconjugated bilirubin, is typically found in the bloodstream. Its name comes from this non-water-soluble bilirubin not reacting directly with reagents added to the samples. Alcohol must be added for the reaction to occur. Indirect bilirubin is increased in cases of hemolytic jaundice, in which the breakdown of hemoglobin results in higher levels of indirect bilirubin. This is the type of bilirubin that is increased in cases of hepatocellular dysfunction such as hepatitis. Usually, only total bilirubin is measured. If total bilirubin is out of range, further testing is done to determine the direct and indirect bilirubin levels.
Possible Interpretations of Pathological Values
- Increase: Biliary obstruction, pancreatic head cancer, choledocholithiasis, cirrhosis, Dubin-Johnson syndrome, hepatitis, obstructive jaundice, pregnancy
Important Note
Laboratory test results are the most critical parameter for diagnosing and monitoring all pathological conditions. Between 70 to 80% of diagnostic decisions are based on laboratory tests. Correctly interpreting laboratory results allows a doctor to distinguish "healthy" from "diseased."
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be analyzed based on each case and family history, clinical findings, and the results of other laboratory tests and information. Your physician should explain the importance of your test results.
At Diagnostiki Athinon, we answer any questions you may have about the test you perform in our laboratory and contact your doctor to ensure you receive the best possible medical care.
