RT Book, Section
A1 Malcolm, William F.
SR Print(0)
ID 1105545203
T1 Hyperbilirubinemia
T2 Beyond the NICU: Comprehensive Care of the High-Risk Infant
YR 2015
FD 2015
PB McGraw-Hill Education
PP New York, NY
SN 978-0-07-174858-2
LK accesspediatrics.mhmedical.com/content.aspx?aid=1105545203
RD 2024/04/23
AB DefinitionJaundiceJaundice  (as  distinct  from  hyperbilirubinemia)  relates  to  the  yellow  color  produced  in  the  sclera,  skin,  and  subcutaneous  tissues  by  deposition  of  bilirubin  in  those  sites.Not  all  jaundiced  newborns  are  necessarily  hyperbiliru-binemic.Visual  assessment  of  jaundice  is  an  inaccurate  way  of  determining  whether  a  baby  is  actually  hyperbilirubinemic,  especially  in  a  premature  infant.HyperbilirubinemiaIn  term  infants,  hyperbilirubinemia  is  frequently  defined  as  a  serum  total  bilirubin  (STB)  concentration  >95th  percentile  on  the  hour-specific  bilirubin  nomogram.In  preterm  infants,  in  contrast,  there  are  no  clear  definitions  of  normal  or  physiologic  bilirubin  levels  and  hence  of  hyperbilirubinemia.  The  reasons  for  this  are  multifold.Almost  all  preterm  infants  develop  some  degree  of  jaundice  during  the  first  postnatal  days.There  are  dynamic  changes  in  STB  levels  during  this  period.The  significance  of  the  jaundice  with  regard  to  bilirubin  neurotoxicity  may  increase  with  decreasing  gestational  age.Phototherapy  is  used  frequently  in  these  infants,  thereby  moderating  STB  values  and  preventing  these  from  reaching  natural  peaks.Practical  definitionsFor  practical  purposes  in  the  preterm  infant  in  the  intensive  care  setting,  we  suggest  the  following,  based  on  the  indications  for  phototherapy  and  exchange  transfusion:Moderate  hyperbilirubinemia:  Includes  any  STB  level  meeting  accepted  criteria  for  phototherapySevere  hyperbilirubinemia:  Regarded  as  any  STB  meeting  or  exceeding  the  indications  for  exchange  transfusionIncidenceAlmost  all  premature  infants  develop  some  degree  of  increased  STB  concentration  that  may  cause  jaundice  and,  in  some  instances,  hyperbilirubinemia.In  the  absence  of  specific  criteria  for  hyperbilirubinemia,  the  incidence  of  the  condition  is  difficult  to  determine.The  majority  of  premature  infants  <1.5  kg  birthweight  will  meet  phototherapy  requirements  during  the  first  postnatal  week.PathophysiologyPhysiology  of  bilirubin  metabolismThe  physiology  of  bilirubin  is  similar  in  the  premature  and  term  infant.Bilirubin  formationRed  blood  cells  are  continually  being  broken  down  in  the  reticuloendothelial  system  and  replaced.  This  process  releases  heme,  which  is  catabolized  by  the  enzyme  heme  oxygenase  1  to  biliverdin  and  thence  to  bilirubin.  This  form  of  bilirubin  is  called  unconjugated  or  indirect  bilirubin.  Bound  to  serum  albumin  the  bilirubin  is  transported  to  the  liver.Bilirubin  conjugation  and  eliminationAfter  uptake  into  the  hepatocyte,  unconjugated  bilirubin  is  glucuronated  to  form  water  soluble  mono-  and  diglucuronides,  known  as  conjugated  or  direct  bilirubin.  The  enzyme  controlling  the  conjugation  process  is  UDP-glucuronosyltransferase  1A1  (UGT).  Direct  bilirubin  is  excreted  via  bile  to  the  bowel  from  which  it  is  excreted  from  the  body.Genetic  control  of  bilirubin  conjugationThe  enzyme  UGT1A1  is  encoded  by  the  gene  UGT1A1.  This  gene  contains  a  noncoding  promoter  region  and  a  coding  region.  Polymorphisms  of  the  promoter  region,  such  as  the  (TA)n  polymorphism,  result  in  diminished  expression  of  a  normally  formed  enzyme  and  are  associated  with  Gilbert  syndrome.  Coding  area  mutations  result  in  an  abnormally  structured  enzyme  with  no  or  little  conjugating  ability,  such  as  is  seen  in  Crigler-Najjar  syndrome.Enterohepatic  circulationIn  the  newborn  bowel,  conjugated  bilirubin  may  be  unconjugated  by  the  enzyme  ?-glucuronidase  and  reabsorbed  into  the  bloodstream,  thereby  adding  to  the  bilirubin  pool  and  straining  the  already  deficient  bilirubin  conjugating  and  elimination  capacity.  Delay  in  enteral  feeding  may  diminish  intestinal  motility,  thereby  decreasing  elimination  via  the  bowel  and  allowing  for  even  greater  reabsorption  of  bilirubin.Significance  of  the  serum  total  bilirubinThe  hallmark  of  hyperbilirubinemia  ...