Bilirubin

This test is used to measure serum levels of bilirubin, the predominant pigment in bile. Bilirubin is the major product of hemoglobin catabolism. Serum bilirubin measurements are especially significant in neonates because elevated unconjugated bilirubin can accumulate in the brain, causing irreparable damage.

Purpose

• To evaluate hepatobiliary and erythropoietic functions
• To aid differential diagnosis of jaundice and monitor its progress
• To aid diagnosis of biliary obstruction and hemolytic anemia
• To determine whether a neonate requires an exchange transfusion or phototherapy because of dangerously high unconjugated bilirubin levels

Patient preparation

• Explain to the patient that this test is used to evaluate liver function and the condition of red blood cells.
• Tell him that the test requires a blood sample. Explain who will perform the venipuncture and when.
• Explain that he may experience slight discomfort from the needle puncture and the tourniquet but that collecting the sample usually takes less than 3 minutes.
• Inform the adult patient that he needn't restrict fluids but should fast for at least 4 hours before the test. (Fasting isn't necessary for neonates.)
• If the patient is an infant, tell the parents that a small amount of blood will be drawn from his heel.
• Tell them who will perform the heelstick and when.

Procedure and posttest care

• If the patient is an adult, perform a venipuncture and collect the sample in a 7-ml red-top or red-marble-top tube.
• If the patient is an infant, perform a heelstick, and fill the microcapillary tube to the designated level with blood.
• If a hematoma develops at the venipuncture or heelstick site, apply warm soaks.

Precautions

• Protect the sample from strong sun­light and ultraviolet light.
• Handle the sample gently, and send it to the laboratory immediately.

Reference values

• In adults, normal indirect serum bilirubin levels are 1 mg/dl or less, and direct serum bilirubin levels are less than 0.2 mg/dl. In neonates, total serum bilirubin levels are 1 to 10 mg/dl.

Abnormal findings

Elevated indirect serum bilirubin levels usually indicate hepatic damage. High levels of indirect bilirubin are also likely in severe hemolytic anemia. If hemolysis continues, both direct and indirect bilirubin levels may rise. Other causes of elevated indirect bilirubin levels include congenital enzyme deficiencies, such as Gilbert's disease.

Elevated direct serum bilirubin levels usually indicate biliary obstruction. If obstruction continues, both direct and indirect bilirubin levels may rise. In severe chronic hepatic damage, direct bilirubin concentrations may return to normal or near-normal levels, but indirect bilirubin levels remain elevated.

In neonates, total bilirubin levels of 18 mg/dl or more indicate the need for an exchange transfusion.

Interfering factors

• Failure to observe pretest restrictions
• Exposure of the sample to direct sunlight or ultraviolet light (possible decrease)
• Hemolysis due to rough handling of the sample
• Failure to send sample to laboratory immediately