Neonatal bilirubin binding capacity discerns risk of neurological dysfunction

Is it time for a precision health approach to the management of newborn hyperbilirubinemia?

Newborn hyperbilirubinemia during the first two weeks of life is one of most common problems requiring management decisions by a pediatrician. However, high bilirubin levels in the circulation have been associated with neurologic injury under a variety of conditions encountered in the newborn infant, such as hemolysis. The risk for developing dangerous hyperbilirubinemia is multifactorial and is determined by a complex set of factors related to a newborn infant's genetic capacities as well as intra- and extrauterine exposures. To this end, a precision health approach based on the integration of prenatal genetic and postnatal diagnostic measures might improve the management of neonatal hyperbilirubinemia.

Use of prophylactic phototherapy for RhD neonatal disease in a referral service

OBJECTIVE

This study aimed to describe the effect of prophylactic phototherapy in the treatment of infants with Neonatal Hemolytic Disease.

METHOD

A retrospective cohort study was carried out with 199 RhD-positive infants, born to RhD-negative mothers, alloimmunized for RhD antigen, between January 2009 and December 2018.

RESULTS

The incidence of exchange transfusions in the study population was 9.5%, with a mean maximum bilirubin value of 11.3 mg % (± 4.3mg %). Bilirubin's maximum peak was achieved with a mean of 119.2 life hours (± 70.6h).

CONCLUSION

The low incidence of exchange transfusion, the extended maximum bilirubin peak for later ages, and the low mean of the maximum bilirubin values may indicate a positive effect of prophylactic phototherapy in the treatment of this disease. Further studies must be carried out to confirm these findings.

Association between neonatal phototherapy and future cancer: an updated systematic review and meta-analysis

Phototherapy is the main treatment of neonatal hyperbilirubinemia to prevent encephalopathy. It is generally believed to be safe; however, some studies have shown it might be associated with cancer development. In this systematic review and meta-analysis, we aimed to assess the effect of neonatal phototherapy on future cancer risk. A systematic search in 13 databases was conducted in December 2018 and updated in August 2022 to identify studies that report cancer development after exposure to phototherapy. Throughout the study period, regular manual searches were also conducted to include new studies. A meta-analysis using R programming language was done in which the odds ratios (ORs) with 95% confidence intervals (CIs) were estimated and pooled using the reported adjusted and unadjusted data. Fifteen studies were included. A statistically significant association was detected between neonatal phototherapy and any type of cancer (OR 1.24; 95% CI 1.1, 1.4), any hematopoietic cancer (OR 1.49; 95% CI 1.17, 1.91), any leukemia (OR 1.35; 95% CI 1.08, 1.67), and myeloid leukemia (OR 2.86; 95% CI 1.4, 5.84). The other investigated cancers (lymphoid leukemia, Hodgkin's lymphoma, kidney cancer, nervous system cancer, and skin cancer) were not associated with phototherapy.  Conclusions: Phototherapy may carry a possible risk of future cancers. Future research is needed to quantify the magnitude of the cancer risk. These future studies should consider predictors of preterm birth or exclude premature babies from their analysis. What is Known • There were various reports about the possible association between phototherapy in neonates and the increased risk of cancer in the future. What is New • A statistically significant association between phototherapy and various hematopoietic cancers (especially myeloid leukemia) was recorded. • The effect of the duration of phototherapy on the increased risk of hematopoietic cancers is yet unclear.

Treatment criteria for infants with hyperbilirubinemia in Japan

With the availability of blue light-emitting diode phototherapy devices capable of delivering high-intensity irradiance, neonatologists in Japan are requesting revisions of the 1992 Kobe University treatment criteria for hyperbilirubinemia using total serum/plasma bilirubin (TB) and serum unbound bilirubin (UB) threshold values, especially for indications for exchange transfusion (ET). Retrospective data analysis of 1,184 infants born between January 2012 and November 2014 when the 1992 criteria were followed, we applied revised criteria proposed in 2017 to these infants to assess consequent changes in treatment recommendations. We found that the estimated number of infants with ET indications decreases from 48 to 20, with intensive phototherapy recommended for the remaining 28. Also, the estimated number of infants with phototherapy indications decreases from 446 to 195. We conclude that use of the revised criteria will lead to judicious use and reduction of phototherapy and ET in infants with hyperbilirubinemia.

Molecular Physiology and Pathophysiology of Bilirubin Handling by the Blood, Liver, Intestine, and Brain in the Newborn

Bilirubin is the end product of heme catabolism formed during a process that involves oxidation-reduction reactions and conserves iron body stores. Unconjugated hyperbilirubinemia is common in newborn infants, but rare later in life. The basic physiology of bilirubin metabolism, such as production, transport, and excretion, has been well described. However, in the neonate, numerous variables related to nutrition, ethnicity, and genetic variants at several metabolic steps may be superimposed on the normal physiological hyperbilirubinemia that occurs in the first week of life and results in bilirubin levels that may be toxic to the brain. Bilirubin exists in several isomeric forms that differ in their polarities and is considered a physiologically important antioxidant. Here we review the chemistry of the bilirubin molecule and its metabolism in the body with a particular focus on the processes that impact the newborn infant, and how differences relative to older children and adults contribute to the risk of developing both acute and long-term neurological sequelae in the newborn infant. The final section deals with the interplay between the brain and bilirubin and its entry, clearance, and accumulation. We conclude with a discussion of the current state of knowledge regarding the mechanism(s) of bilirubin neurotoxicity.

Pathogenesis and Management of Indirect Hyperbilirubinemia in Preterm Neonates Less Than 35 Weeks: Moving Toward a Standardized Approach

Premature infants have a higher incidence of indirect hyperbilirubinemia than term infants. Management of neonatal indirect hyperbilirubinemia in late preterm and term neonates has been well addressed by recognized, consensus-based guidelines. However, the extension of these guidelines to the preterm population has been an area of uncertainty because of limited evidence. This leads to variation in clinical practice and lack of recognition of the spectrum of bilirubin-induced neurologic dysfunction (BIND) in this population. Preterm infants are metabolically immature and at higher risk for BIND at lower bilirubin levels than their term counterparts. Early use of phototherapy to eliminate BIND and minimize the need for exchange transfusion is the goal of treatment in premature neonates. Although considered relatively safe, phototherapy does have side effects, and some NICUs tend to overuse phototherapy. In this review, we describe the epidemiology and pathophysiology of BIND in preterm neonates, and discuss our approach to standardized management of indirect hyperbilirubinemia in the vulnerable preterm population. The proposed treatment charts suggest early use of phototherapy in preterm neonates with the aim of reducing exposure to high irradiance levels, minimizing the need for exchange transfusions, and preventing BIND. The charts are pragmatic and have additional curves for stopping phototherapy and escalating its intensity. Having a standardized approach would support future research and quality improvement initiatives that examine dose and duration of phototherapy exposure with relation to outcomes.

A multi-center evaluation of a device for measurement of bilirubin binding capacity in neonates: the effects of gestational age, Intralipid exposure and illness severity

OBJECTIVE

Measure daily bilirubin-binding capacity (BBC) variation using an automated, not as-yet FDA approved, Point-of-Care hematofluorometer. Measure the effects of prematurity, clinical instability and exposure to Intralipid on BBC.

SUBJECTS

Convenience sample of 109 infants from well-baby and intensive care nurseries. Gestational ages 28-41 weeks. 261 specimens obtained from postnatal ages 1-4 days. Unstable neonates were defined by need for at least noninvasive respiratory support and FiO2 ≥ 0.25.

RESULTS

Median interday variation was 2.9 ± 5.1 mg/dL. BBC (0.254 mg/dL/wk) and albumin (0.037 g/dL/wk) increased for each week of gestation. BBC was lower in unstable compared to well infants (26.1 ± 7.6 mg/dL v 28.6 ± 6.3 mg/dL). BBC was not significantly different in infants receiving or not receiving IL.

CONCLUSIONS

BBC measurements using the device had acceptable intraspecimen reproducibility and interday variability. BBC may be helpful in guiding the assessment of aggressive versus conservative management decisions in preterm and sick infants with hyperbilirubinemia.

Bilirubin binding in jaundiced newborns: from bench to bedside?

BACKGROUND

Bilirubin-induced neurologic dysfunction (BIND) is a spectrum of preventable neurological sequelae in jaundiced newborns. Current total plasma bilirubin (B_T) concentration thresholds for phototherapy and/or exchange transfusion poorly predict BIND.

METHODS

The unbound (free) bilirubin (B_f) measured at these B_T thresholds provides additional information about the risk for BIND. B_f can be readily adapted to clinical use by determining B_f population parameters at current B_T thresholds. These parameters can be established using a plasma bilirubin binding panel (BBP) consisting of B_T, B_f, and two empiric constants, the maximum B_T (B_Tmax) and the corresponding equilibrium association bilirubin constant (K).

RESULTS

B_Tmax and K provide the variables needed to accurately estimate B_f at B_T < B_Tmax to obtain B_f at threshold B_T in patient samples. Once B_f population parameters are known, the BBP in a newborn can be used to identify poor bilirubin binding (higher B_f at the threshold B_T compared with the population) and increased risk of BIND.

CONCLUSION

The BBP can also be used in jaundice screening to better identify the actual B_T at which intervention would be prudent. The BBP is used with current B_T thresholds to better identify the risk of BIND and whether and when to intervene.

Jack Aviv and brains of children

Both lead intoxication in early childhood and deficient bilirubin-binding capacity (BBC) of blood in jaundiced neonates indicate risk for brain damage. Zinc protoporphyrin (ZPP) is a biomarker for lead intoxication (PbI) as well as well as for iron deficiency. Under the leadership of Jack Aviv, Aviv Biomedical, Inc. developed robust hematofluorometers for point-of-care assays of ZPP in blood and for the high-affinity BBC of blood. These assays use just drops of whole blood and are simple, fast and inexpensive. ZPP by hematofluorometry has been used world-wide as a primary screen for lead intoxication since 1979. Recent clinical studies enabled by an Aviv Biomedical, Inc. bilirubin hematofluorometer have renewed interest in BBC-based assessment of neurotoxicity for improved management of neonatal jaundice. This article sketches Jack Aviv's contribution to the development and application of hematofluorometry.

Effects of Soybean Lipid Infusion on Unbound Free Fatty Acids and Unbound Bilirubin in Preterm Infants

OBJECTIVE

To assess the effects of a soybean lipid emulsion infusions on levels of unbound (free) bilirubin (Bf) and unbound free fatty acids (FFAu) as well as changes in Bf and total serum bilirubin (TSB) during phototherapy in infants born preterm.

STUDY DESIGN

Ninety-seven infants born preterm (birth weight: 500-2000 g; gestational age: 23-34 weeks) were enrolled to investigate the effect of 0, 1, 2, and 3 g/kg/d of intralipid infusion on Bf and FFAu. Pre- and postphototherapy TSB, FFAu, and Bf also were analyzed in 91 infants to assess the effects of phototherapy. FFAu levels were measured with the fluorescent probe ADIFAB2 and Bf by the fluorescent Bf sensor BL22P1B11-Rh during intralipid infusion and at start and end of phototherapy. TSB and plasma albumin were measured by the diazo and bromcresol green techniques, respectively. Bilirubin-albumin dissociation constants were calculated based on Bf and plasma albumin.

RESULTS

Bf and FFAu increased with increasing intralipid dosage across all gestational ages. TSB and Bf were correlated significantly when infants received 0 or 1 g/kg/d of intralipid but not at greater doses of intralipid (2 and 3 g/kg/d). Although phototherapy effectively reduced both TSB and Bf in the total phototherapy group (by 32% and 12%, respectively), it reduced TSB, but not Bf, in infants less than 28 weeks of gestation.

CONCLUSIONS

Increasing intralipid doses result in increasing FFAu levels, which are associated with increased Bf independent of TSB. In infants born extremely preterm (<28 weeks of gestation), phototherapy effectively reduces TSB but not Bf.

The Bilirubin Binding Panel: A Henderson-Hasselbalch Approach to Neonatal Hyperbilirubinemia

Poor plasma bilirubin binding increases the risk of bilirubin neurotoxicity in newborns with hyperbilirubinemia. New laboratory tests may soon make it possible to obtain a complete bilirubin binding panel when evaluating these babies. The 3 measured components of the panel are the plasma total bilirubin concentration (B_Total), which is currently used to guide clinical care; the bilirubin binding capacity (BBC); and the concentration of non-albumin bound or free bilirubin (B_Free). The fourth component is the bilirubin-albumin equilibrium dissociation constant, K_D, which is calculated from B_Total, BBC, and B_Free The bilirubin binding panel is comparable to the panel of components used in the Henderson-Hasselbalch approach to acid-base assessment. Bilirubin binding population parameters (not prospective studies to determine whether the new bilirubin binding panel components are better predictors of bilirubin neurotoxicity than B_Total) are needed to expedite the clinical use of bilirubin binding. At any B_Total, the B_Free and the relative risk of bilirubin neurotoxicity increase as the K_D/BBC ratio increases (ie, bilirubin binding worsens). Comparing the K_D/BBC ratio of newborns with B_Total of concern with that typical for the population helps determine whether the risk of bilirubin neurotoxicity varies significantly from the inherent risk at that B_Total Furthermore, the bilirubin binding panel individualizes care because it helps to determine how aggressive intervention should be at any B_Total, irrespective of whether it is above or below established B_Total guidelines. The bilirubin binding panel may reduce anxiety, costs, unnecessary treatment, and the likelihood of undetected bilirubin neurotoxicity.

A Pharmacologic View of Phototherapy

A pharmacologic view of phototherapy for neonatal jaundice is presented. By considering the photons of therapy light as molecules of a drug, this view connects therapeutic efficacy with photon wavelength, photon dose, dose rate and regimen, efficiency of photon absorption by bilirubin, quantum yields of photoproducts, and their metabolic courses. Based on this view, recommendations to ultimately improve efficacy and safety are presented. Special attention is given to phototherapy regimens for low gestational age, low birthweight infants.

Bilirubin Binding Capacity in the Preterm Neonate

Total serum/plasma bilirubin (TB), the biochemical measure currently used to evaluate and manage hyperbilirubinemia, is not a useful predictor of bilirubin-induced neurotoxicity in premature infants. Altered bilirubin-albumin binding in premature infants limits the usefulness of TB in premature infants. In this article, bilirubin-albumin binding, a modifying factor for bilirubin-induced neurotoxicity, in premature infants is reviewed.

Hyperbilirubinemia in Preterm Neonates

Preterm neonates with increased bilirubin production loads are more likely to sustain adverse outcomes due to either neurotoxicity or overtreatment with phototherapy and/or exchange transfusion. Clinicians should rely on expert consensus opinions to guide timely and effective interventions until there is better evidence to refine bilirubin-induced neurologic dysfunction or benefits of bilirubin. In this article, we review the evolving evidence for bilirubin-induced brain injury in preterm infants and highlight the clinical approaches that minimize the risk of bilirubin neurotoxicity.

Phototherapy and the Risk of Photo-Oxidative Injury in Extremely Low Birth Weight Infants

Phototherapy has been used to treat newborns with jaundice for more than 50 years with the presumption that it is safe and effective for all infants. In fact, this presumption may not be true for all infants, especially the smallest and most immature. The safety and efficacy of phototherapy have never really been questioned or adequately tested in the latter, yet clinical applications of phototherapy have been further refined as its mechanisms of action have been better understood and alternative light sources have become available. This article addresses what is known about the possible risks of photo-oxidative injury in extremely low birth weight infants.

Identification of neonatal haemolysis: an approach to predischarge management of neonatal hyperbilirubinemia

AIM

Relative contributions of increased production [by end-tidal carbon monoxide concentrations (ETCOc)] and decreased elimination of bilirubin to predischarge hour-specific total bilirubin (TB) levels were assessed in healthy late-preterm and term newborns. Secondly, we report predischarge ETCOc ranges to guide clinical management of hyperbilirubinemia.

METHODS

TB and ETCOc (≤3 timepoints) determinations of newborns aged between six hours and <6 days (n = 79) were stratified by postnatal age epochs. Hyperbilirubinemia risk was assessed by plotting TB values as a function of ETCOc.

RESULTS

Stratifications of ETCOc (in ppm, mean, median and interquartile ranges) by postnatal age epochs (0-24, 24-48 and 48-72) were as follows: 2.0, 1.9, 1.8-2.2 (n = 11); 1.6, 1.5, 1.1-2.0 (n = 58); and 2.0, 1.8, 1.6-2.3 (n = 9), respectively. Infants with ETCOc ≥ 2.5 were at high risk, between 1.5 and 2.5 at moderate risk and ≤1.5 were at low risk. Risk due to haemolysis alone was not independent (p < 0.01). For infants with TB >75th percentile (n = 31), 23% had ETCO ≤1.5, and 77% had ETCOc > 1.5 (p < 0.00003).

CONCLUSION

Near-simultaneous ETCOc and TB measurements in infants with TB >75th percentile accurately identify haemolytic hyperbilirubinemia.