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Test Code LAB4027 BILIRUBIN, TOTAL

Important Note

Useful for:

  • Assessing liver function
  • Evaluating a wide range of diseases affecting the production, uptake, storage, metabolism, or excretion of bilirubin

Additional Codes

Labcorp 001099

Specimen Type

Preferred Sample: Lithium Heparin Plasma (PST, Mint Green Tube)
Alternative Sample:  Serum (Gold SST, Corvac, Tiger, Red Top Tube)

Collection Instructions

Protect from light

Specimen Processing

Separate serum from cells within 2 hours of collection. Protect from light.

Rejection Criteria

Hemolyzed samples

Specimen Volume

Preferred: 1.0 mL

Minimum: 0.5 mL

Sample Stability

Room Temperature: 1 day

Refrigerated: 7 days

Frozen: 3 Months

Clinical Information

Bilirubin is a degradation product of hemoglobin. Red blood cells at the end of their circulating lives are broken down in the reticuloendothelial system, mainly the spleen. The resulting heme is converted to bilirubin upon removal of iron. This process accounts for about 80% of bilirubin formed daily. Other sources of bilirubin include the breakdown of myoglobin and cytochromes and the catabolism of immature red blood cells in the bone marrow. Once formed, bilirubin is transported to the liver bound to albumin. Bilirubin bound to albumin is insoluble in water and is known as unconjugated (indirect) bilirubin. In the liver, unconjugated bilirubin is coupled with glucuronide; this form is called conjugated (direct) bilirubin. It is water soluble and is mostly excreted in bile.

 

The sum of direct and indirect bilirubin is called total bilirubin and the indirect fraction of the total usually makes up to approximately 85%. In cases of hyperbilirubinemia, bile pigment is deposited in the skin, sclera, and mucous membranes and so the patient has yellowish color; this condition is called jaundice or icterus. In newborns or in people with familial hyperbilirubinemia the presence of jaundice and elevation of total bilirubin may indicate inherited metabolic disorders.

 

Fractionation of total bilirubin into conjugated and unconjugated may help in the diagnosis of hyperbilirubinemia. For example, conjugated bilirubin is increased in cases of cholestasis caused by several liver diseases (e.g., hepatitis, hepatic obstruction, and cirrhosis), while a high level of unconjugated bilirubin may indicate a hemolytic disorder. Inherited metabolic disorders may also have differences in conjugated and unconjugated fractions: increased conjugated bilirubin suggests Dubin-Johnson or Rotor syndromes, while unconjugated bilirubin is prevalent in Gilbert, Crigler-Najjar, or Lucey-Driscoll syndromes. The total bilirubin test is used as an aid in the differential diagnosis and management of liver diseases, and neonatal jaundice, as well as hemolytic, and inherited metabolic diseases.

 

Neonatal bilirubin quantitation is also used to monitor diseases causing jaundice in the newborn, chiefly erythroblastosis fetalis (also called hemolytic disease of the newborn or HDN). HDN is caused by maternal alloimmunization to RhD, antibodies involving additional blood groups, and ABO incompatibility. The average full-term newborn infant has a peak serum bilirubin concentration of 5 to 6 mg/dL. Physiologic jaundice is seen at serum bilirubin concentrations from 7 to 17 mg/dL. Serum bilirubin concentrations greater than 17 mg/dL may be pathologic. The primary concern is the potential for bilirubin encephalopathy or severe jaundice.

Method

Photometric/Diazonium Salt

 

Diazonium Salt Traditional methods of measuring bilirubin are based on the reaction of bilirubin with a diazo reagent to form the colored compound azobilirubin. The diazo reaction can be accelerated by the addition of various chemicals. For example, Malloy-Evelyn used methanol, Jendrassik-Gróf used caffeine, and Walters-Gerarde used dimethyl sulfoxide (DMSO). Modifications of these methods included the addition of surfactants as solubilizing agents. Total (conjugated and unconjugated) bilirubin couples with a diazo reagent in the presence of a surfactant to form azobilirubin. The diazo reaction is accelerated by the addition of surfactant as a solubilizing agent. The increase in absorbance at 548 nm due to azobilirubin is directly proportional to the total bilirubin concentration.

Limitations

  • Interferences from medication or endogenous substances may affect results.
  • Specimens should be protected from bright light as bilirubin is photolabile. 
  • In samples where the concentration of bilirubin is low, or where conjugated bilirubin is the predominant form, the Direct Bilirubin assay may report results that are greater than results obtained using the Total Bilirubin assay.
  • Specimens with indocyanine green levels greater than 5 mg/L may cause falsely elevated results with the Total Bilirubin2 assay.
  • Specimens with indican levels greater than 1 mg/dL may cause falsely elevated results with the Total Bilirubin2 assay.
  • The assay runs using an initial standard dilution of 1:1.97 to achieve the AMR.

Turnaround Time

STAT: 1 hour
Routine: 4 hours

Reference Ranges

Bilirubin, total, mg/dL
0 up to 7 Days Refer to bilitool.org
7 days up to 15 Days 0.2 - 16.6
15 Days up to 1 Year <0.8
1 year up to 9 Years <0.5
9 years up to 12 Years <0.7
12 years up to 15 Years <0.8
15 years up to 19 Years <0.9
19 Years and older 0.3 - 1.2

Components

Bilirubin, Total mg/dL

 

Measuring Range 0.1 – 25.0 mg/dL

Reporting Limits 0.1 – 125.0 mg/dL

 

*If result after a 1:5 dilution is greater than 125.0 mg/dL, report out >125.0 mg/dL.

Test Schedule

Daily and STAT

CPT Codes

82247