The approximate normal range of bilirubin in the blood serum is:
- 1.2 milligrams per deciliter (mg/dL) for adults
- 1 mg/dL for children under 18 years of age
The skin normally becomes yellow once levels reach between 2 and 3 mg/dL.
Any person who experiences yellowing of the skin or eyes should see their doctor. It may be a sign of a serious condition.
Blood tests can measure bilirubin levels. While there is a urine test for bilirubin, it is less accurate and often falsely positive.
If a routine urine test detects bilirubin, a doctor will look at blood serum tests to confirm the results and identify any damage to the liver.
Other tests include:
- further blood tests to assess liver function and test for hepatitis, if indicated
- a physical exam, where a doctor may feel the abdominal area to see if the liver is enlarged or tender.
- imaging tests to visualize the liver. These might include ultrasound, computerized X-ray with a CT scan, or high-powered images with an MRI scan.
- an endoscopy is sometimes carried out to look at the ducts in which the bile travels to the gut.
- a liver biopsy is sometimes needed, although this is uncommon. In this procedure, a small sample of liver tissue is sent to a lab for evaluation.
High bilirubin levels
High bilirubin levels can cause jaundice. Jaundice makes the skin and the whites of the eyes appear yellow, due to the brown and yellow bilirubin in the blood. There are several reasons for a rise in bilirubin levels outside the newborn period. These causes can occur before, during, or after the production of bilirubin.
What is bilirubin?
The breakdown of red blood cells (RBCs) in the body produces bilirubin. The bilirubin travels to the liver and is stored in the bile duct. The body ultimately expels bilirubin in stools.
The RBCs have a lifespan of around 120 days and renew continually. RBCs contain hemoglobin, which helps transport oxygen around the body, and it is this that gets broken down into bilirubin and other substances. The bilirubin is carried to the liver by albumin, a simple protein.
Once in the liver, bilirubin becomes “conjugated.” This means it becomes water-soluble and can be excreted.
Unconjugated bilirubin is toxic, but conjugated bilirubin is usually not, because it can be removed from the body, as long as nothing is interfering with its removal.
Before reaching the liver
Some conditions cause bilirubin levels to be high before it reaches the liver.
This is the pre-hepatic or “pre-liver” phase, and it can be caused by hemolytic anemia and the reabsorption of internal pools of blood by the body. Hemolytic anemia occurs when too many red blood cells are broken down before the end of their natural life cycle.
In the liver
If the liver is not working properly, it may be unable to make bilirubin water-soluble. This may result in too much bilirubin building up in the liver.
Causes include, but are not limited to the following: viruses, such as hepatitis A. alcoholic liver disease some medicine overdoses, including acetaminophen autoimmunity, where a disorder of the immune system causes it to attack the cells of the body rather than those that cause disease
Once the bilirubin has left the liver, levels may be high because the bilirubin is unable to leave the body. This may be a result of blockage in one of the other organs that assist excretion, such as gallstonesin the gallbladder. This is called the post-hepatic phase. Other causes include: inflammation or cancer of the gallbladder, which produces bilepancreatitis.
A bilirubin test measures total bilirubin. It can also give levels of two different types of bilirubin: unconjugated and conjugated.
Unconjugated (“indirect”) bilirubin. This is the bilirubin created from red blood cell breakdown. It travels in the blood to the liver.
Conjugated (“direct”) bilirubin. This is the bilirubin once it reaches the liver and undergoes a chemical change. It moves to the intestines before being removed through your stool.
For adults over 18, normal total bilirubin can be up to 1.2 milligrams per deciliter (mg/dl) of blood. For those under 18, the normal level will be will be 1 mg/dl. Normal results for conjugated (direct) bilirubin should be less than 0.3 mg/dl.
Men tend to have slightly higher bilirubin levels than women. African-Americans tend to have lower bilirubin levels than people of other races.
High total bilirubin that is mostly unconjugated (indirect) may be caused by:
- A reaction to a blood transfusion
- Gilbert syndrome — a common, inherited condition in which there is a deficiency of an enzyme that helps to break down bilirubin.
- Viral hepatitis
- A reaction to drugs
- Alcoholic liver disease
Strenuous exercise can increase your bilirubin levels.
Caffeine, penicillin, barbiturates, and nonsteroidal anti-inflammatory drugs (NSAIDs) called salicylates all lower your bilirubin levels. Lower-than-normal levels of bilirubin aren’t usually a problem, but better to check with health provider.
In newborns, high bilirubin levels that don’t level out in a few days to 2 weeks may be a sign of:
- Blood type incompatibility between mother and child
- Lack of oxygen
- An inherited infection
- A disease affecting the liver
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