When does bilirubin (a yellow compound that occurs in the normal catabolic pathway that breaks down heme in red blood cells) level decrease?

From the Guidelines

Bilirubin levels decrease within 4 to 6 hours of initiation of phototherapy in newborns with hyperbilirubinemia, as evidenced by a decrease in total serum or plasma bilirubin concentrations. This is supported by the most recent and highest quality study, which found that with proper administration of effective phototherapy, total serum or plasma bilirubin concentrations will decrease within the first 4 to 6 hours of initiation safely and effectively 1.

Key Factors Influencing Bilirubin Decrease

• The rate of decline in bilirubin levels depends on factors such as the intensity of phototherapy, the presence of hemolysis, and the gestational age of the infant 1.
• Phototherapy works by converting bilirubin into water-soluble forms that can be excreted without liver processing, with the most significant decline occurring in the first 4 to 6 hours 1.
• In addition to phototherapy, addressing the underlying cause of hyperbilirubinemia, such as treating hemolytic conditions or biliary obstructions, is crucial for reducing bilirubin levels 1.

Clinical Implications

• Serial measurements of bilirubin concentration are used to monitor the effectiveness of phototherapy, with the goal of reducing the risk of bilirubin neurotoxicity 1.
• The decision to discontinue phototherapy should be individualized, taking into account the TSB level at which phototherapy was initiated, the cause of the hyperbilirubinemia, and the risk of rebound hyperbilirubinemia 1.
• Adequate hydration supports bilirubin excretion in all cases, and is an important adjunct to phototherapy and other treatments for hyperbilirubinemia.

From the Research

Bilirubin Decrease

• Bilirubin levels can decrease with the use of phototherapy, as it is universally recognized as the first option for treating neonatal jaundice due to its efficiency and safety in reducing high serum free bilirubin levels 2.
• The combination of phenobarbital and phototherapy can enhance the decline of total serum bilirubin and may decrease the need for blood exchange transfusion in newborns with isoimmune hemolytic disease 3.
• Phenobarbitone can reduce peak serum bilirubin, duration and need of phototherapy, and need of exchange transfusion in preterm very low birthweight neonates 4.
• Low plasma bilirubin levels, defined as "hypobilirubinemia", are a possible new pathology analogous to the other end of the spectrum of extreme hyperbilirubinemia seen in patients with jaundice and liver dysfunction 5.
• The evaluation of patients with jaundice, which is associated with hyperbilirubinemia, starts with a careful history and physical examination, followed by directed imaging of the biliary tree and liver 6.

Timing of Bilirubin Decrease

• The difference between the mean total serum bilirubin levels at 24,48, and 72 hours after starting the trial was clinically and statistically significant, indicating a decrease in bilirubin levels within 24-72 hours 3.
• The duration of phototherapy was shorter with the use of phenobarbitone, indicating a faster decline in total serum bilirubin 4.

Factors Influencing Bilirubin Decrease

• Phototherapy is a key factor in reducing high serum free bilirubin levels 2.
• The combination of phenobarbital and phototherapy can enhance the decline of total serum bilirubin 3.
• Phenobarbitone can reduce peak serum bilirubin, duration and need of phototherapy, and need of exchange transfusion in preterm very low birthweight neonates 4.