NICHD Conference on Kernicterus: Research on Prevention of Bilirubin-Induced Brain Injury and Kernicterus: Bench-to-Bedside--Diagnostic Methods and Prevention and Treatment Strategies

The Genetics of Glucose-6-Phosphate-Dehydrogenase (G6PD) and Uridine Diphosphate Glucuronosyl Transferase 1A1 (UGT1A1) Promoter Gene Polymorphism in Relation to Quantitative Biochemical G6PD Activity Measurement and Neonatal Hyperbilirubinemia

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and polymorphism in uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) were associated with significant neonatal hyperbilirubinemia (NHB) and increased risk for kernicterus. However, quantitative screening tests for G6PD enzyme activity proved unsatisfactory in estimating the risk for significant NHB, especially in heterozygous females that could present phenotype overlap between normal homozygotes, heterozygotes, and deficient homozygotes, resulting in a continuum of intermediate G6PD activity.

OBJECTIVE

To examine the association of genotype and phenotype in newborns with decreased G6PD activity and its relation to NHB.

STUDY DESIGN

Quantitative G6PD enzyme activities were measured on umbilical cord blood samples. After accepting parental consent, samples were analyzed for G6PD mutations and UGT1A1 gene polymorphisms (number of TA repeats in the UGT1A1 promoter). The associations to quantitative G6PD activity and bilirubin levels were assessed.

RESULTS

28 females and 27 males were studied. The Mediterranean mutation (NM_001360016.2(G6PD): c.563C>T (p.Ser188Phe)) was responsible for most cases of G6PD deficiency (20 hemizygous males, 3 homozygous and 16 heterozygous females). The association between this mutation, decreased G6PD activity and higher bilirubin levels was confirmed. Heterozygosity to 6/7 TA repeats in the UGT1A1 promoter was associated with increased NHB, especially in female newborns with G6PD deficiency. However, it seems that the interaction between G6PD deficiency, UGT1A1 promoter polymorphism, and NHB is more complex, possibly involving other genetic interactions, not yet described. Despite genotyping females with G6PD deficiency, the overlap between the upper range of borderline and the lower range of normal G6PD activity could not be resolved.

CONCLUSIONS

The results of this study highlight the possibility for future implementation of molecular genetic screening to identify infants at risk for significant NHB, especially UGT1A1 polymorphism in heterozygous females with borderline G6PD deficiency. However, further studies are needed before such screening could be applicable to daily practice.

Predictability of transcutaneous bilirubinometry in late preterm and term infants at risk for pathological hyperbilirubinemia

BACKGROUND

The aim was to assess the predictability of transcutaneous bilirubinometry in late preterm and term neonates at risk for pathological hyperbilirubinemia, and to identify the neonatal population in which transcutaneous bilirubin most accurately predicts serum bilirubin level (SB, mg/dl).

METHODS

The correlations between transcutaneous bilirubin (TCB, mg/dl) and SB in different neonatal population subsets; and between ΔTSB (TCB-SB) and relevant neonatal variables and clinical groups were analyzed.

RESULTS

TCB correlated with SB (r = 0.82, p < 0.05) in the cohort (n = 350) and in population subsets (r = 0.81-0.9, p < 0.001). Black infants with gestational age (GA) >35 weeks and chronological age (CA) >3 days recorded strongest correlation (r = 0.9, p < 0.001) followed by Blacks, and non-Black infants with CA >3 days and GA >35 weeks. ΔTSB was positive in Blacks, and in infants with CA <3 days, or with no phototherapy. ΔTSB was negative in non-Blacks, in infants with positive direct Coombs test (DC+) or those receiving phototherapy. Black race [beta (SE) = 1.3(0.33), p < 0.001] had positive, while CA [beta (SE) =-1.74 (0.36), p < 0.001], DC + status [beta (SE) =-0.72 (0.25), p = 0.004] and receipt of phototherapy [beta (SE) =-0.84 (0.21), p < 0.001] each had negative correlation with ΔTSB. ΔTSB for Blacks was >Whites, Hispanics and Asians.

CONCLUSION

SB is best predicted by TCB in Black infants with CA over 3 days and GA over 35 weeks. Variability in SB estimation by TCB is race, CA and immune mediated hemolysis specific.

Hyperbilirubinemia and Transcutaneous Bilirubinometry

Background: Neonatal jaundice or hyperbilirubinemia is a common occurrence in newborns. Although most cases of neonatal jaundice have a benign course, severe hyperbilirubinemia can lead to kernicterus, which is preventable if the hyperbilirubinemia is identified early and treated appropriately.

Content: This review discusses neonatal jaundice and the use of transcutaneous bilirubin (TcB) measurements for identification of neonates at risk of severe hyperbilirubinemia. Such a practice requires appropriate serial testing and result interpretation according to risk level from a nomogram that provides bilirubin concentrations specific for the age of the neonate in hours. In this context, we have evaluated the potential impact on clinical outcome and limitations of TcB methods in current use.

Summary: TcB measurement is a viable option in screening neonates to determine if they are at risk for clinically significant hyperbilirubinemia. Total serum bilirubin should be measured by a clinical laboratory if a newborn is shown to be at higher risk for clinically significant hyperbilirubinemia. In addition, external quality assessment to identify biases and operator training issues should be part of any TcB monitoring program.

Clinical report from the pilot USA Kernicterus Registry (1992 to 2004)

To identify antecedent clinical and health services events in infants (>/=35 weeks gestational age (GA)) who were discharged as healthy from their place of birth and subsequently sustained kernicterus. We conducted a root-cause analysis of a convenience sample of 125 infants >/=35 weeks GA cared for in US healthcare facilities (including off-shore US military bases). These cases were voluntarily reported to the Pilot USA Kernicterus Registry (1992 to 2004) and met the eligibility criteria of acute bilirubin encephalopathy (ABE) and/or post-icteric sequelae. Multiple providers at multiple sites managed this cohort of infants for their newborn jaundice and progressive hyperbilirubinemia. Clinical signs of ABE, verbalized by parents, were often inadequately elicited or recorded and often not recognized as an emergency. Clinical signs of ABE were reported in 7 of 125 infants with a subsequent diagnosis of kernicterus who were not re-evaluated or treated for hyperbilirubinemia, although jaundice was noted at outpatient visits. The remaining infants (n=118) had total serum bilirubin (TSB) levels >20 mg per 100 ml (342 micromol l(-1); range: 20.7 to 59.9 mg per 100 ml). No specific TSB threshold coincided with onset of ABE. Of infants <37 weeks GA with kernicterus, 34.9% were LGA (large for gestational age) as compared with 24.7% of term infants (>37 weeks GA). Although >90% mothers initiated breast-feeding, assessment of milk transfer and lactation support was suboptimal in most. Mortality was 4% (5 of 125) in infants readmitted at age </=1 week. Along with a rapid rise of TSB (>0.2 mg per 100 ml per hour), contributing factors, alone or in combination, included undiagnosed hemolytic disease, excessive bilirubin production related to extra-vascular hemolysis and delayed bilirubin elimination (including increased enterohepatic circulation, diagnosed and undiagnosed genetic disorders) in the context of known late prematurity (<37 weeks), glucose 6-phosphate-dehydrogenase deficiency, infection and dehydration. Readmission was at age </=5 days in 81 of 118 (69%) infants and <10 days in 101 of 118 (86%) infants. TSB levels were </=35 mg per 100 ml (598 micromol l(-1)) in 46 (39%) infants, of whom one died before exchange transfusion, one was untreated and one was lost to follow-up. Timely and efficacious bilirubin reduction interventions defined by 'crash-cart' initiation of immediate intensive phototherapy and urgent exchange transfusion were accomplished in 11 of 43 infants, which were compared with 12 of 43 infants in whom a timely exchange sometimes could not be accomplished. No overt sequelae were found in 8 of 11 infants (73%) treated with a 'crash-cart' approach compared with none without sequelae when exchange was delayed by pre-admission delays, technical factors or need to transfer to a tertiary facility. None of the remaining 20 of 43 infants treated only with phototherapy escaped sequelae. Regardless of age at readmission and intervention, infants with peak measured TSB >35 mg per 100 ml had post-icteric sequelae (n=73). There was a narrow margin of safety between birthing hospital discharge or home birth and readmission to a tertiary neonatal/pediatric facility. Progression of hyperbilirubinemia to hazardous levels and onset of neurological signs were often not identified as infant's care and medical supervision transitioned during the first week after birth. The major underlying root cause for kernicterus was systems failure of services by multiple providers at multiple sites and inability to identify the at-risk infant and manage severe hyperbilirubinemia in a timely manner.

Point of care testing: transcutaneous bilirubinometry in neonates

Physicians taking care of infants in the first days of life are often faced with neonatal jaundice, especially in an era where post-partum discharge occurs earlier and assessment of newborn bilirubinemia status is required prior to discharge. The Canadian Pediatric Society and the American Academy of Pediatrics have developed and published guidelines for the diagnosis and management of hyperbilirubinemia in newborns. Point of care testing refers to any test performed outside of laboratory by clinical personnel and close to the site of patient care. Based on a summary of multiple reports during the last twenty years, we realize that devices which provide a non-invasive transcutaneous bilirubin (TcB) measurement have proven to be very useful as screening tools and provide a valid estimate of the total serum bilirubin level (TSB). Published data suggest that these devices provide measurements within 30-50 micromol/L of the TSB levels and can replace laboratory measurement particularly when TSB levels are less than 260 micromol/L. At the present time, in the literature, evidence is insufficient to abandon neonatal serum bilirubin testing and replace it with TcB. Any measurement, TSB or TcB, has potential for error. However, we have evidence that TcB, can help avoiding potential errors associated with even visual assessment of jaundice and may be useful as screening device to detect significant jaundice and decrease a large number of unnecessary skin punctures. The current manuscript is based on a careful comprehensive literature review concerning neonatal hyperbilirubinemia. We consider that this manuscript will help clinicians and laboratory professionals in the management of neonatal jaundice.

Management of jaundice and prevention of severe neonatal hyperbilirubinemia in infants >or=35 weeks gestation

Kernicterus is still occurring but should be largely preventable if health care personnel follow the recommendations listed in this guideline. These recommendations emphasize the importance of universal, systematic assessment of the risk of severe hyperbilirubinemia, lactation support, close follow-up, and prompt intervention when necessary. A systems-based approach to prevent severe neonatal hyperbilirubinemia should be implemented at all birthing facilities and coordinated with continuing ambulatory care. Translational research is needed to better understand the mechanisms of bilirubin neurotoxicity and potential therapeutic interventions.

Investigating jaundice in the newborn

JAUNDICE IS OFTEN SEEN IN the neonatal period, with 60 percent of full-term and 80 percent of preterm infants having visible jaundice.1 Jaundice is a sign of hyperbilirubinemia, which, in the newborn period, is usually due to an elevated indirect or unconjugated bilirubin level, and may result from an exaggerated physiologic response or be pathologic in nature. Hyperibilirubinemia due to an elevated direct or conjugated bilirubin is less common. Although an elevated direct bilirubin level can be transient, it is often related to some pathology.

Measurement of unbound bilirubin by the peroxidase test using Zone Fluidics

BACKGROUND

Measuring plasma unbound bilirubin concentration by the peroxidase test is useful in the management of jaundiced newborns. However, the commercially available peroxidase technology is manual, and the unbound bilirubin may be seriously underestimated at the 42-fold sample dilution and single peroxidase concentration used. We investigated improving the test by adapting it to Zone Fluidics, which is a system for automating reactant handling that requires small sample volumes and dilution.

METHODS

A computer-directed Zone Fluidics system was constructed using small diameter tubing to connect in series a water-surfactant reservoir, a bi-directional pump, a multiport selection valve to which peroxidase test reactants (45 mul of sample) are attached with one port open to air, and a spectrophotometer flow cell. Test reactants and air are sequentially aspirated through the valve into the tubing connecting the pump and valve to form a reactant "zone" surrounded by air. The zone is advanced to the spectrophotometer flow cell where total and unbound bilirubin are determined (37 degrees C) from the absorbance at 460 nm at a 2-fold sample dilution and 4 peroxidase concentrations. Imprecision was assessed in artificial controls and newborn plasma. Plasma results were compared with those obtained using the commercial method.

RESULTS

The CV for unbound bilirubin in the various controls ranged from 11% to 38% (within day) and 12% to 27% (between days). Triplicate CV measurements for newborn plasma measurements ranged from 0.6% to 31% (mean 11%, n=47). Mean unbound bilirubin by Zone Fluidics was 5-fold higher than that by the commercial method.

CONCLUSION

Zone Fluidics can be used to automate the peroxidase test and overcome many of the limitations of the commercially available peroxidase technology.

Evaluation of a model for brain bilirubin uptake in jaundiced newborns

A model for brain bilirubin uptake (BBU) predicts that BBU in jaundiced newborns typically depends on the plasma total bilirubin concentration (TBC) and the bilirubin-albumin dissociation rate constant (k1) rather than the unbound bilirubin (Bf). The model's validity was tested by 1) evaluating its requirement that k3>>>k2, where k3 and k2 are the rate constants for BBU and Bf-albumin association, respectively, and 2) determining whether the calculated BBU is <or=5% of the bilirubin production rate, the approximate BBU expected if brain bilirubin levels are <1% of the miscible bilirubin pool as reported in the literature. The model was investigated using peroxidase test measurements of TBC, Bf, k1, and k2 from 185 jaundiced newborns. Mean k2 was compared with the reported k3 value of 0.08/s. BBU calculated from TBC and k1 was expected to be <or=0.005 microg/kg/s given the reported bilirubin production rate of 0.1 microg/kg/s. BBU calculated using Bf was also compared with the bilirubin production rate. The mean k2 of 8.9 L/micromol/s was greater than k3, and the mean BBU of 0.72 microg/kg/s exceeded the expected range of <or=0.005 microg/kg/s. However, mean BBU using Bf (0.00073 microg/kg/s) was within the expected range. A mathematical model calculating BBU as a function of TBC and k1 could not be validated. BBU calculated from Bf is consistent with the observation that <1% of the miscible bilirubin pool is distributed in the brain.

Immunizations, neonatal jaundice, and animal-induced injuries

PURPOSE OF REVIEW

To concisely review data published over the past year on three topics pertinent to the practicing pediatrician: immunizations, neonatal jaundice, and animal-induced injuries.

RECENT FINDINGS

Updates on immunizations, including varicella and pneumococcus in the post-vaccine era, use of a polyvalent conjugated meningococcal vaccine, and influenza vaccination during a vaccine shortage are discussed. Mortality and morbidity from varicella, and risk of invasive disease from pneumococcal infections have declined. The Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention released guidelines for the use of a tetravalent meningococcal conjugate vaccine in adolescents 11 years and older. Infants at younger gestational age are at higher risk for developing hyperbilirubinemia. The American Academy of Pediatrics has released new guidelines emphasizing breastfeeding, systematic pre-discharge assessment for risk factors, early follow-up and intervention. Use of home nursing services in the postnatal period is cost-effective. Although the incidence of rabies is low, many receive postexposure prophylaxis. Spider bites cause fewer systemic effects in children than adults. Pet reptile carriage of salmonella necessitates handwashing after handling of animals.

SUMMARY

Recommendations for adolescent meningococcal vaccination, and the impact of varicella and pneumococcal immunization on our communities reflect an evolution in our management of infectious diseases. The latest practice guidelines on hyperbilirubinemia emphasize close follow-up of all newborns after postpartum discharge and even more careful evaluation of those infants near term. Education on rabies prophylaxis, spider bites, and salmonella from pet reptiles should focus on judicious use of resources and the proper handling of pets.