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Pathology Lab uses both traditional methods
and new technology
to measure fractionated bilirubin
By Gregory J. Buffone, Ph.D. with forward written by Michael E. Speer, M.D.
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Texas Children's Hospital Pathology Laboratory measures
total bilirubin using the traditional Jendrasik-Groff assay,
while BU and BC fractions are measured using the newer
technology.
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Forward: Hsia et al1 reported that 50 percent of infants with rh isoimmunization and total serum bilirubin (TSB) greater than 30 mg/dL developed kernicterus, while more than 200 similar infants with total serum bilirubin levels less than 20mg/dL did not. The authors concluded that “although it has not been proved that bilirubin is the actual cause of brain damage, tests of serum bilirubin in infants with erythroblastosis fetalis serve as extremely valuable guides to treatment.” Since that report, the search for effective strategies to limit the incidence of kernicterus has been ongoing. All have used the total serum value of bilirubin as the measurement of choice, including the recent guidelines2 developed by the American Academy of Pediatrics (AAP), even though this method may overestimate the amount of unconjugated bilirubin. Diseases of the liver benefit from a more precise estimation of function. Thus, the measurement of conjugative function (conjugated and unconjugated bilirubin) is valuable in following diseases such as viral hepatitis or bile cholestasis.
The Chemistry section of the Pathology Laboratory is now routinely offering total bilirubin (BT) in addition to conjugated (BC) and unconjugated (BU) in response to recent guidelines promulgated by the AAP –
Management of Hyperbilirubinemia in the Newborn Infant 35 or More Weeks of Gestation. The guideline recommends measurement of BT as the preferred means of assessing risk of kernicterus in the first seven days of life.
Traditional methods for the analysis of bilirubin provided a crude fractionation of the total bilirubin, reported as direct and indirect (BI, calculated result). Newer, more accurate methods provide interference free results, as well as allowing the quantitation of bilirubin covalently bound to albumin (Bd), a form that cannot readily cross the blood-brain barrier. For reasons too lengthy to enumerate in this memo, the newer methods used to fractionate bilirubin do not produce results that can be added or subtracted from BT in a manner similar to the traditional assays, e.g., BI = BT – BC or BT = BC + BI. Texas Children's Hospital Pathology Laboratory measures total bilirubin using the traditional Jendrasik-Groff assay, while BU and BC fractions are measured using the newer technology. As such, you will note that in many instances the sum of BU and BC may not equal BT. Please note, this difference is not the result of analytical error.
Bilirubin measurement may be ordered in the following combinations: BT only, BC and BU or as a Bilirubin Panel that includes BT and BC. If the order for testing is ambiguous, the laboratory will perform a Bilirubin Panel.
Where to find more information
A short article describing the analytical and clinical considerations related to
bilirubin fractionation is provided for your reference on the
Pathology Online Catalog in the Quick Reference, Chemistry section. An electronic copy of the
Bhutani Nomogram, recommended by the AAP guideline for assessing risk of kernicterus on the basis of the BT concentration, can also be found in this section of the Online Catalog. The Pathology Online Catalog can be reached from the Texas Children's Hospital
Intranet home page.
Direct any questions to Dr. Ching Ou, director of Clinical Chemistry, at 832-824-5107 or Dr. Gregory Buffone at 832-824-5105.
Gregory J. Buffone, Ph.D., is director of Laboratories, Department of Pathology, at Texas Children's Hospital and a professor of Pathology at Baylor College of Medicine. Michael E. Speer, M.D., is medical director of Quality and Outcomes Management and a member of the Neonatology medical staff at Texas Children’s, as well as a professor of Pediatrics at Baylor.
1. Hsia D, Allen F, Cellis S, Diamond L. Erythroblastosis fetalis. VIII. Studies of serum bilirubin in relation to kernicterus. N Engl J Med. 1952;247 :668 –67.
2. Subcommittee on Hyperbilirubinemia. Management of Hyperbilirubinemia in the Newborn Infant 35 or More Weeks of Gestation. Pediatrics 114 (1) : 297-316.
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