Serum or plasma concentration of total bilirubin

A bilirubin test measures the level of bilirubin, a yellow pigment your body produces when old red blood cells break down, in your blood. This test matters because it helps your doctor check how well your liver is working, whether red blood cells are being destroyed too quickly, and whether bile is draining properly from the liver. It is often ordered to investigate jaundice, fatigue, dark urine, or belly pain, and to monitor known liver conditions such as hepatitis or cirrhosis.

Bilirubin is normally filtered by your liver and excreted through bile into your intestines. If your liver isn’t working properly, bilirubin can build up in your blood, leading to yellowing of the skin and eyes (jaundice). This test helps doctors identify whether your symptoms are due to liver disease, gallbladder problems, or other conditions.

The test is a simple blood draw, usually taken from a vein in your arm. A healthcare professional will clean the site, place a band around your upper arm, and collect a small sample into a tube. The sample goes to a laboratory, where the total bilirubin level is measured and sometimes broken down into direct and indirect portions. Results are reported in mg/dL and are typically ready within one to two days.

A small blood sample is taken and analyzed to measure bilirubin levels. The test can be performed on serum (liquid part of blood after clotting) or plasma (liquid part of blood without clotting). The result is expressed in a standardized unit (e.g., micromoles per liter).

High bilirubin levels can be caused by liver diseases such as hepatitis, cirrhosis, or blocked bile ducts from gallstones or tumors, as well as by conditions that speed up red blood cell breakdown, like hemolytic anemia. Certain medications, including some antibiotics and chemotherapy drugs, can also raise levels. Low bilirubin levels are usually not a concern and may be related to medications such as barbiturates, to caffeine, or simply to normal individual variation. Your doctor will interpret your result together with your symptoms and other tests.

High bilirubin levels (hyperbilirubinemia) may occur due to liver diseases (like hepatitis), bile duct obstructions (e.g., gallstones), hemolytic anemia (rapid red blood cell destruction), or certain medications. Low levels are less common but may occur in rare genetic conditions or severe liver damage.

Most people need no special preparation for a bilirubin blood test, and you can usually eat and drink normally beforehand. If the test is part of a larger panel of liver tests, your doctor may ask you to fast for several hours. Tell your provider about all medications, supplements, and herbal products you take, since some can affect the results. Drinking water before your appointment can make the blood draw easier. The procedure takes only a few minutes, and you can return to your normal activities right afterward.

No special preparation is needed for this test. You may have a small needle inserted into your arm to draw blood. If you’re nervous, let your healthcare provider know—they can help make the process more comfortable.