A recent case report published in Clinical Laboratory describes an infant with jaundiceJaundice A common symptom of HDFN, jaundice is caused by excess bilirubin and is characterized by a yellow tint to the skin or eyes. who was treated with phototherapyPhototherapy A treatment that uses special blue light to help newborns break down bilirubin and prevent kernicterus. and received seemingly nonsensical bilirubinBilirubin A yellow substance produced when red blood cells break down. High bilirubin levels in newborns with HDFN can cause jaundice or, in severe cases, brain damage. testing results after treatment.
Phototherapy is a common treatment for babies with hemolytic disease of the fetus and newborn (HDFN) and severe jaundice. Special lights are used help to remove excess bilirubin from the body. However, as this case report suggests, certain laboratory tests for bilirubin may be inaccurate due to the chemical changes in bilirubin’s structure caused by phototherapy.
What is bilirubin?
Bilirubin is a molecular byproduct of the breakdown of hemoglobin, the protein responsible for holding the oxygen transported in red blood cells. It is normally transported to the liver, where it undergoes a transformation called conjugation, and is then excreted from the body through the intestines. Jaundice is caused by the accumulation of bilirubin in the blood, which is known as hyperbilirubinemiaHyperbilirubinemia A common cause of jaundice, this refers to higher than normal bilirubin levels in the blood..
The authors describe a five-day-old female who presented with hyperbilirubinemia and blood pooling under the scalp. Besides yellowing skin, she had no notable symptoms.
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Bilirubin can be classified as either conjugated or unconjugated, depending on its structure. Initial testing revealed that the neonate’s total bilirubin level was 352.4 μmol/L. However, her unconjugated bilirubin level was somehow higher than the total level at 388.1 μmol/L, and the conjugated bilirublin level was 13.5 μmol/L. This paradoxical result prompted further investigation in the laboratory.
The laboratory results showed during phototherapy, unconjugated bilirubin can take on one of two different structural forms, which may be measured inaccurately depending on which technique is used.
The researchers repeated bilirubin testing using a different method. The total bilirubin level was 355.4 μmol/L, aligning with the previous result. Her unconjugated bilirubin was now measured as 338.7 μmol/L, and conjugated bilirubin was measured as 16.7 μmol/L.
The investigators point out that differences in how laboratories process samples can also contribute to discrepancies. Therefore, they recommend that physicians focus on the individual unconjugated and conjugated bilirubin levels when making clinical decisions.
“Laboratories must adopt standardized reporting practices and educate clinicians on methodological constraints,” the authors concluded. “Clinicians should use consistent methods for serial monitoring, and laboratories must analyze pre-analytical factors, such as phototherapy timing, to ensure accurate reporting.”
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