Bilirubin, Serum

CPT CODE:

USEFUL FOR:

Assessing liver function
Evaluating a wide range of diseases affecting the production, uptake,storage, metabolism, or excretion of bilirubin
Monitoring the efficacy of neonatal phototherapy

SPECIMEN REQUIRED:

Draw blood in a plain, red-top tube(s) or a serum gel tube(s). Spin down and send 1.0 mL of serum (pediatric: 0.5mL) refrigerated or frozen in amber vial (# Supply T192) to protect from light.Note:    Patient's age and sex are required on request                   form for processing.

TRANSPORT TEMPERATURE:

Refrig\Frozen OK\Ambient NO

CLINICAL INFORMATION:

Bilirubin is one of the most commonly used tests to assess liver function.Approximately 85% of the total bilirubin produced is derived from theheme moiety of hemoglobin, while the remaining 15% is produced fromred blood cell precursors destroyed in the bone marrow and from thecatabolism of other heme-containing proteins. After production inperipheral tissues, bilirubin is rapidly taken up by hepatocytes whereit is conjugated with glucuronic acid to produce bilirubin mono- anddiglucuronide, which are then excreted in the bile.
A number of inherited and acquired diseases affect one or more of the steps involved in the production, uptake, storage, metabolism, andexcretion of bilirubin. Bilirubinemia is frequently a direct result of thesedisturbances.
The most commonly occurring form of unconjugated hyperbilirubinemiais that seen in newborns and referred to as physiological jaundice.
The increased production of bilirubin that accompanies the premature breakdown of erythrocytes and ineffective erythropoiesis results in hyperbilirubinemia in the absence of any liver abnormality.
The rare genetic disorders, Crigler-Najjar syndromes Type I andType II, are caused by a low or absent activity of bilirubin UDP-glucuronyl-transferase. In Type I, the enzyme activity istotally absent, the excretion rate of bilirubin is greatly reducedand the serum concentration of unconjugated bilirubin is greatlyincreased. Patients with this disease may die in infancy owing tothe development of kernicterus.
In hepatobiliary diseases of various causes, bilirubin uptake, storage, and excretion are impaired to varying degrees. Thus, both conjugated and unconjugated bilirubin are retained and a wide range of abnormal serum concentrations of each form of bilirubin may be observed. Both conjugated and unconjugated bilirubins are increased in hepatitis and space-occupying lesions of the liver; and obstructive lesions such as carcinoma of the head of the pancreas, common bile duct, or ampulla of Vater.

CLINICAL INTERPRETATION:

The level of bilirubinemia that results in kernicterus in a given infant isunknown. In preterm infants, the risk of a handicap increases by 30% for each 2.9 mg/dL increase of maximal total bilirubin concentration.While central nervous system damage is rare when total serum bilirubin (TSB) is <20 mg/dL, premature infants may be affected at lower levels. The decision to institute therapy is based on a number of factors including TSB, age, clinical history, physical examination, and coexisting conditions. Phototherapy typically is discontinued when TSB level reaches 14 to 15 mg/dL.
Physiologic jaundice should resolve in 5 to 10 days in full-term infantsand by 14 days in preterm infants.
When any portion of the biliary tree becomes blocked, bilirubin levelswill increase. 

REFERENCE VALUES:

DIRECT

      0-11 months:  not established

      > or = 1 year:  0.0-0.3 mg/dL

TOTAL

   Males

      0-11 months:  not established

      1 year:  0.1-0.9 mg/dL

      > or =2 years:  0.1-1.0 mg/dL

   Females

      0-11 months:  not established

      1-11 years:  0.1-0.9 mg/dL

      > or =12 years:  0.1-1.0 mg/dL