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Revista chilena de pediatría

versión impresa ISSN 0370-4106

Rev. chil. pediatr. vol.90 no.3 Santiago jun. 2019 


Severe hyperbilirubinemia in newborns, risk factors and neurological outcomes

Stephanie Campbell Wagemann1 

Patricia Mena Nannig2 

1 Resident of Neonatology, Department of Neonatology, School of Medicine, Pontificia Universidad Católica de Chile, Chile.

2 Neonatology Service of Dr. Sótero del Río Asistencial Complex, and Department of Neonatology, School of Medicine, Pontificia Universidad Católica de Chile, Chile.



Hyperbilirubinemia is highly prevalent in newborns, with risk of neurological invol vement with bilirubinemia higher than 20 to 25 mg/dl. This progression is preventable with early de tection and treatment.


To describe the incidence and associated factors in hospitalized pa tients with hyperbilirubinemia higher than 20 mg/dl, and the follow-up of symptomatic cases during hospitalization.

Patients and Method:

Retrospective study of patients with severe hyperbilirubine mia, between 2013 and 2016. Risk factors were evaluated, stratifying by bilirubin level, admission age, and gestational age. The data were compared with Fisher’s exact test, chi-square test, and relative risk (RR) in an Excel database, with an alpha error of p <0.05. The data were obtained from the electronic discharge summary and the medical record of secondary level follow-up.


During the studied period, out of 25,288 live newborns (NB), 593 were hospitalized due to hyperbilirubinemia higher than 20 mg/dl, one per each 42 live NB; and 59 with bilirubinemia higher than 25 mg/dl, one per each 428 live NB. Hyperbilirubinemia was more frequent in males, with RR 1.22 (95% CI 1.04-1.44), and in late preterm newborns, with RR 2.39 (95% CI 1.96-2.93) compared with term NB. In those admitted with more than four days, the main associated factor was excessive weight loss, whereas in the first three days was classic group incompatibility. Three of ten cases with acute encephalopathy persisted with neurological involvement, which means 11.8 per 100,000 live births.


The main risk factors for developing severe hyperbilirubinemia were prematurity, excessive weight loss, classic group incompatibility, and male sex. These findings allow to focus attention on risk groups and decrease the probability of neurological damage.

Keywords: Severe hyperbilirubinemia; prematurity; bilirubin encephalopathy; classic group incompatibility


Jaundice is highly prevalent in the newborn (NB), affecting up to 60-80% of newborns1,2,3. It is considered hyperbilirubinemia (HBR) when serum bilirubin level is higher than the 95th percentile for age, and it is ge nerally considered severe when levels exceed 20 or 25 mg/dl4,5.

Bilirubin is an important antioxidant, which has a fine regulatory system that maintains stable levels, but it can be affected by different causes, leading to a bilirubin increase6. As bilirubin levels increase, the re is a risk of developing neurological toxicity or bi lirubin encephalopathy. This spectrum includes acu te and chronic bilirubin encephalopathy and isolated neurologic dysfunction7. Acute encephalopathy can range from weak suction to severe neurological invol vement with deep stupor and opisthotonos. Chronic encephalopathy or kernicterus is a devastating neuro logical entity characterized by athetoid cerebral palsy, with oculomotor paresis, dental enamel dysplasia, and auditory neuropathy8-11. The auditory system is parti cularly sensitive to the bilirubin effects, ranging from speech processing disturbances to profound deafness. Hearing damage due to bilirubin requires a time win dow, occurring when cells are developing the forma tion of the neuronal circuits, thus premature infants are at greater risk. In addition, sensory pathways are myelinated before motor pathways, leading to a more common observation of kernicterus with predominant hearing damage in children under 34 weeks, in con trast to the classic motor type which is more frequent in term NBs7,12,27. This may occur at levels that were not previously considered harmful, but in general, with bi lirubin levels higher than 20 mg/dl, long-term hearing follow-up is necessary6,7,12. It has been described that more than half of NBs with bilirubin higher than 30 mg/dl develop neurological sequelae26.

Phototherapy and exchange transfusion have led to a reduction in acute and chronic bilirubin encephalo- pathy6,9. With the Rh isoimmunization prevention, the use of immunoglobulin and the phototherapy effecti veness, the need for exchange transfusion, which is an invasive procedure, not risk-free, has been markedly reduced4,9.

Despite the existence of efficient treatment, the se vere HBR risk and its consequences are observed with a wide range of incidence worldwide, depending on the used control strategies4,9,13,14.

The objective of this study is to describe the inci dence and risk factors associated with bilirubinemia equal to or higher than 20 mg/dl, and the evolution of patients with signs of bilirubin encephalopathy during hospitalization, compared with data in the li terature.

Patients and Method

Descriptive, retrospective study. Based on infor mation from the electronic discharge database, we included newborns hospitalized in the Neonatology service of the Dr. Sótero del Río Asistencial Complex (SRAC) between January 1, 2013 and December 31, 2016, with a discharge diagnosis of hyperbilirubinemia and a maximum value of total serum bilirubin higher than or equal to 20 mg/dl. With this information, we reviewed the discharge summary of the newborns. NBs whose electronic discharge summary could not be ac cessed were excluded.

During the study period, bilirubin levels were analyzed using the same method, Total Bilirubin: end- point/Diazonium salt.

NBs were stratified by bilirubin values in two levels, higher than or equal to 20 mg/dl, and higher than or equal to 25 mg/dl; by age of admission, as less than or equal to three days, between 4 and 7 days, and higher than or equal to 8 days; and by gestational age. (Table 1) shows the risk factors for severe hyperbilirubinemia that were evaluated, such as sex, gestational age, bir th weight adequacy, excessive weight loss, group and Rh incompatibility, cephalhematoma, polycythemia, sepsis, perinatal asphyxia, urinary tract infection, and hypothyroidism.

Table 1 Definitions. 

Presence of neurological symptoms during hospi talization, compatible with acute bilirubin encephalo pathy was recorded, and the outpatient child neurolo gy care data in the SRH of these patients were reviewed.

Data were compared with Fisher’s exact test, chi- square, and relative risk (RR) in an Excel database, with a p<0.05 alpha error.

The study was reviewed and approved by the Ethics and Research Committee of the South-East Metropo litan Health Service.


In the studied period, there were 25,288 live new borns (LNB), 48.3% female and 51.6% male. 599 NBs were hospitalized with bilirubin levels higher than or equal to 20 mg/dl, of which six cases were excluded, as there was no access to electronic discharge summary. In the 593 cases left, 2.3% of incidence (1 in 42 LNB) was observed. 59 NBs had bilirubin levels higher than or equal to 25 mg/dl, with 0.23% of incidence (1 in 428 LNB). 53 NBs (9% of cases) were rehospitalized due to severe HBR, six of them had bilirubin levels higher than 20 mg/dl in both hospitalizations.

Out of the total of patients, 80.6% were term new borns, 18.7% were late preterm newborns, and 0.7% were moderate ones. There were no cases of severe hy perbilirubinemia in NBs under 32 weeks of gestational age.

(Figure 1) describes the bilirubinemia risk between 20 and 24.9 mg/dl and higher than 25 mg/dl, depen ding on the gestational age at birth. The highest biliru- binemia risk between 20 and 25 mg/dl was seen at 35 weeks (1 in 16 NBs of that gestational age), and higher than 25 mg/dl at 36 weeks (1 in 85 NBs). Compared with term NBs, preterm infants are at higher risk of se vere HBR, with RR 1.78 (95% CI 1.45-2.17), especially late preterm infants, between 34 and 36 weeks, with RR 2.39 (95% CI 1.96-2.93).

Figure 1 Risk of severe hy perbilirubinemia (%) between 20-25 mg/dl and more than 25 mg/dl according to gesta tional age. 

(Table 2) shows the characteristics of the group ac cording to age at hospitalization and associated cau ses. 19.4% of the cases were under 37 weeks. Globally, the male sex presents a higher risk than the female sex, with a RR of 1.22 (95% CI 1.04-1.44) and it also in creases with days of presentation. Cases of hyperbiliru binemia higher than 25 mg/dl were mostly observed in children under 8 days of life.

Table 2 Main characteristics of NBs hospitalized by severe hyperbilirubinemia, according to age of admission. 

In NBs hospitalized before 4 days of age, the main risk factor was classical group incompatibility, with a RR of 3.78 (95% CI 1.84-7.78). In NBs hospitali zed from 4 days of life, the most important risk fac tor was excessive weight loss, with RR 2.61 (95% CI 1.74-3.92) in NBs between 4 and 7 days, and RR 6.71 (95% CI 4.59-9.81) in those older than or equal to 8 days of age.

44 cases were analyzed for urinary tract infection and 27% of them had positive urine culture. A case of hypothyroidism stands out for its importance. In 75 NBs (12.6%) more than one risk factor was associated, with prematurity and excessive weight loss more fre quently observed.

Other risk factors, such as birth weight adequacy, cephalohematoma , polycythemia, sepsis, or asphyxia were not associated with increased risk of severe HBR.

All hospitalized NBs due to severe HBR received phototherapy, 16 NBs received immunoglobulin, and 12 exchange transfusion. Out of the NBs who received immunoglobulin, three cases corresponded to rehos pitalizations, who received this drug during the first hospitalization.

Table 3 describes the subgroup with HBR higher than 25mg/dl in the same admission periods, with hig her predominance of male sex and incompatibility.

Table 3 Main characteristics of NBs hospitalized by hyperbilirubinemia > 25 mg/dl, according to age of admission. 

Ten of 59 NBs with bilirubin levels equal to or hig her than 25 mg/dl had an abnormal neurological exam. Mild hypotonia was described in two cases, mild hy pertonia in six cases, and encephalopathy in two cases, which determines a 0.04% acute bilirubin encephalo pathy incidence in the total NBs. (Table 4) describes the cases and their associated factors. Two patients have normal MRI results. In five cases exchange transfusion was performed, in the other cases, bilirubin levels de creased significantly with the first hours of photothera py and hydration. There is no follow-up in two cases, and in three cases there is a clinical picture compatible with chronic bilirubin encephalopathy, with an inci dence of 11.8/100,000 newborns.

Table 4 Cases of acute bilirubin encephalopathy and neurological evolution. 


Severe hyperbilirubinemia, defined as levels of total bilirubin higher than 25 mg/dl in a term newborn or higher than 20 mg/dl in a premature infant older than or equal to 34 weeks of gestation, represents a risk fac tor for the appearance of neurotoxicity and sequelae secondary to the nerve tissue impregnation by biliru bin, in which visual and hearing disorders, and signs of extrapyramidal cerebral palsy stand out4,6,8,9,21,22. It’s a permanent concern in neonatology.

The severe HBR incidence was surprisingly high, from almost double to 40 times that described in the literature in developed countries5,10,21. In the global analysis, 1 case in 47 NBs with HBR between 20-25 mg/dl was observed; and 1 in 428 NBs with HBR hig her than 25 mg/dl. California data show bilirubinemia higher than 20 mg/dl in 1 of 72 LNBs, and higher than 25 mg/dl in 1 of 1430 LNB29. In developed countries, between 1/2,000 - 1/10,000 cases of NBs with HBR hig her than 25 mg/dl have been observed, and 1/18,000 NBs have even been reported in Israel, which has fluid coordination with primary care and a detailed pro tocol for prevention and detection28. In low-income countries, such as countries from Africa and Asia, the reported HBR incidence higher than 25 mg/dl varies between 4 and 46%23. We did not find information on its incidence in Latin America.

The main risk factors for developing severe HBR were male sex, prematurity, excessive weight loss, and classic group incompatibility. The highest risk group is late preterm infants, between 34-36 weeks of gesta tional age, who have a RR of 2.39 (95% CI 1.96- 2.93) regarding term infants, similar to that described in the literature9,10,15-17,23,24.

The maximum bilirubin increase in term NBs oc curs between 3 to 5 days of age when the NB has al ready been discharged, thus follow-up in at-risk chil dren is important. In addition, the maximum loss of normal weight occurs on the third day, with an average loss between 6 and 8% of birth weight. In newborns who have lost more than 10% of weight, evaluation is necessary to eventually supplement breastfeeding and evaluate the presence of HBR3,9.

The relationship between HBR and urinary tract infection is not yet fully understood. It has been des cribed that about 8% of HBR in which no cause can be found, present urinary tract infection, especially due to Escherichia coli25. Due to the retrospective nature of the work, urine culture was not found in all patients, the-refore, it is not possible to determine the urinary tract infection incidence in this group. Urine culture was positive in 27% of the evaluated cases and constitutes an important morbidity to rule out in late hyperbili rubinemia that has suggestive symptoms such as fever, weight loss, and procalcitonin alteration.

The evaluation of hypothyroidism should be reser ved for the case without elements that explain hyper bilirubinemia and especially if there are elements of a primary defect, which is not detectable with screening.

Twelve cases required exchange transfusion, 47/100,000 LNB, compared to 1.9 to 3.6/100,000 LNB in California22. Of the ten symptomatic cases, only five were treated with exchange transfusion, since while it was being prepared, a significant decrease in bilirubin was observed, or the neurological alteration was later, but when facing a symptomatic case, the recommen ded therapy is the exchange transfusion15.

Although acute neonatal bilirubin encephalopathy has decreased dramatically due to adequate control and treatment of the mother with Rh-negative blood type to prevent sensitization, there is some risk increa se with the early discharges rise, lack of warning to pa rents about the risk of hyperbilirubinemia, and lack of timely control at the outpatient level, especially of pa tients at risk, such as late premature infants and early term NBs7,9,26. In addition, neurological and hearing alterations may be transitory or late onset, so short and long term follow-up of NBs exposed to high bilirubin levels is very important7.

Acute and chronic encephalopathy incidence has decreased significantly. An incidence of 0.3 to 1 in 10,000 LNB has been estimated for acute encephalo pathy and around 1 in 100,000 for chronic type(49>13>14). In this review, 4 cases in 10,000 of acute encephalo pathy and 11.8 cases in 100,000 of chronic encepha lopathy were observed. There are no national data on chronic bilirubin encephalopathy, but a national pu blication shows that it has not disappeared30.

The limitations of this study are that it is retros pective and data were obtained from discharge sum maries, where information could have been omitted, such as searching for other diagnoses if the cause of hy perbilirubinemia was unclear. The admission date was not necessarily due to hyperbilirubinemia, and weight loss corresponds to the minimum observed weight. Interesting data such as the feeding type before hos pitalization and the mother’s perception of jaundice were not available. All cases of hyperbilirubinemia hig her than 25 mg/dl are referred to child neurology and a healthcare center to follow up encephalopathy, but short-term non-attendance and lack of a rescue system has prevented complete patient information. Out of the 10 identified patients with signs of acute encephalopathy, follow-up information was obtained of eight of them, and among them, there is one case identified with chronic encephalopathy and two probable cases.

The strength of this study is to show that the risk of neurological damage due to bilirubin is still occu rring, therefore, an early HBR detection and treatment is important. Severe hyperbilirubinemia is a sentinel event that must be avoided. Therefore, it is necessary to establish regulations to follow according to gesta tional age, hours of life, and the pertinent follow-up, different from those previously used, broadening the control ranges. Late preterm newborns must be mo nitored for bilirubin levels at discharge, regardless of jaundice and follow-up.

The determination of transcutaneous bilirubin in serial form using known nomograms would alert es pecially when there are important changes in levels31. For late risk, it is necessary greater coordination with the primary level and early follow-up after discharge, especially of late premature infants, whose follow- up should be before 72 hours of the discharge, as has been pointed out in the new childcare program of the Ministry of Health32. With the installation of a survei llance and intervention system, the risk of severe hy perbilirubinemia and its potential sequelae could be reduced28,29.

In conclusion, the severe HBR incidence in this period was unacceptably high. The main risk factors for developing severe HBR were male sex, prematurity, excessive weight loss, and classic group incompatibili ty. Clinical practices to control bilirubinemia should be modified, especially for late preterm infants, high criteria for phototherapy and establish a prospective protocol for surveillance of severe HBR, which due to its consequences, should be considered as a sentinel event watched nationally.

Ethical Responsibilities

Human Beings and animals protection: Disclosure the authors state that the procedures were followed ac cording to the Declaration of Helsinki and the World Medical Association regarding human experimenta tion developed for the medical community.

Data confidentiality: The authors state that they have followed the protocols of their Center and Local regu lations on the publication of patient data.

Rights to privacy and informed consent: The authors state that the information has been obtained anony mously from previous data, therefore, Research Ethics Committee, in its discretion, has exempted from ob taining an informed consent, which is recorded in the respective form.

Financial Disclosure: Authors state that no economic support has been asso ciated with the present study.

Conflicts of Interest: Authors declare no conflict of interest regarding the present study.


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Received: June 11, 2018; Accepted: December 07, 2018

Correspondence: Patricia Mena Nannig. E-mail:

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