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Details of Bilirubin Direct
What is Bilirubin?
Also Known As: Total Serum Bilirubin TSB Total Bilirubin TBIL Neonatal Bilirubin Direct Bilirubin Conjugated Bilirubin Indirect Bilirubin Unconjugated Bilirubin
Formal Name: Bilirubin - blood
Bilirubin is a dark yellow waste product that is primarily created when the body breaks down hemoglobin, which is the protein in red blood cells that carries oxygen. Bilirubin is found in bile, which is fluid in your liver that is involved in digesting food. Most bilirubin is eliminated in the feces or urine.
The bilirubin test checks the health of your liver by measuring the amount of bilirubin in blood or in your urine. This can help diagnose or monitor problems related to your liver or red blood cells when the bilirubin level is too high.
Purpose of the test
Doctors often order a bilirubin test along with other tests performed on a single blood or urine sample, such as in a comprehensive metabolic panel, a liver panel, or a urinalysis.
Testing bilirubin in the blood and urine can help doctors diagnose problems such as jaundice, a condition that may cause your eyes and skin to turn yellow, as well as hepatitis, cirrhosis, gallbladder disease, and hemolytic anemia.
Bilirubin blood testing is also used to diagnose newborn jaundice which can lead to a condition called kernicterus at very high bilirubin levels. Prolonged and very high bilirubin levels can lead to complications if left untreated, so testing is commonly performed in newborns during their first few days of life and when signs of jaundice appear.
In people who have been diagnosed with a liver disorder, repeated bilirubin testing can help a doctor monitor the status of the patient’s disease and how they are responding to treatment.
What does the test measure?
The bilirubin blood test measures the amount of bilirubin in the blood. Results are commonly expressed as mg/dL, or milligrams of bilirubin per deciliter of blood.
Bilirubin mainly exists in two forms in the blood. Initially, bilirubin is “unconjugated.” Unconjugated bilirubin is bilirubin attached to albumin, the main protein in blood that carries substances to the liver.
In the liver, bilirubin undergoes a process called conjugation with a substance called glucuronide, through which bilirubin becomes “conjugated.” Conjugated bilirubin is water-soluble and ready to be excreted into bile.
A total bilirubin blood test includes unconjugated and conjugated bilirubin. Due to the uniqueness of the analytical measurement of bilirubin, unconjugated bilirubin may also be called indirect bilirubin while conjugated bilirubin may also be referred to as direct bilirubin.
Another less common bilirubin measurement, called delta bilirubin, is only formed when the excretion of conjugated bilirubin by the liver is impaired. This can happen when a patient suffers from a bile duct obstruction. This type of conjugated bilirubin is linked to albumin and may persist for a prolonged period of time in your blood.
Neonatal bilirubin is commonly assessed in newborns and refers to the marked elevation of total bilirubin mainly due to the increase in unconjugated bilirubin. Typically, a newborn’s liver needs a few days to take over the clearance of the bilirubin by conjugating bilirubin. This leads to increased bilirubin levels which then reach normal levels about one week after birth.
The urinary bilirubin test measures whether or not bilirubin is present in the urine.
How to get tested
Bilirubin testing is typically conducted in a medical setting after being ordered by a doctor.
If you are being evaluated for a liver condition or red blood cell disorder, your doctor may also order other tests, including blood or urine tests, an ultrasound, or a biopsy.