Yield of reticulocyte counts and blood smears in term infants

Immunohematology testing using umbilical cord blood: review of the literature, survey of practice and guidance development

BACKGROUND

Following delivery, blood tests are performed on umbilical cord blood (CB) to avoid neonatal venipuncture. Despite widespread and longstanding CB testing, no guidelines exist to suggest which immunohematology tests should be performed on CB.

STUDY DESIGN AND METHODS

We performed a scoping review, surveyed national practice, and developed guidance statements concerning CB testing. Database searches identified relevant articles. A survey was sent to all Canadian hospitals and transfusion laboratories that perform perinatal testing. A national panel of experts was convened to develop guidance statements.

RESULTS

A total of 116 articles met the inclusion criteria and were summarized. Literature on CB testing is limited; few studies have investigated laboratory testing methodologies or validated CB test results with peripheral samples. The survey was completed by 580/597 institutions (97%); 85% were community hospitals and 16% had a neonatal intensive care unit. There is diversity in the types of CB tests performed and variability in practice. While most centers order appropriately, some laboratories routinely perform CB tests that are not clinically indicated (e.g., direct antiglobulin testing for all neonates) and other do not perform CB tests when results would be beneficial (e.g., phenotype on CB when mother has a clinically significant antibody). Fifteen guidance statements were developed.

DISCUSSION

This study highlights variability in CB testing, likely reflecting evidence gaps, methodology differences between studies, and lack of guidelines. CB tests should only be performed when indicated and validated on this sample type. The presented guidance statements aim to standardize practice and encourage judicious CB sampling.

Neonatal jaundice: aetiology, diagnosis and treatment

A significant proportion of term and preterm infants develop neonatal jaundice. Jaundice in an otherwise healthy term infant is the most common reason for readmission to hospital. Jaundice is caused by an increase in serum bilirubin levels, largely as a result of breakdown of red blood cells. Bilirubin is conveyed in the blood as 'unconjugated' bilirubin, largely bound to albumin. The liver converts bilirubin into a conjugated form which is excreted in the bile. Very high levels of unconjugated bilirubin are neurotoxic. Phototherapy is a simple and effective way to reduce the bilirubin level. Most term babies have 'physiological' jaundice which responds to a short period of phototherapy, and requires no other treatment. A few babies have rapidly rising bilirubin levels which place them at risk of kernicterus. Current management of jaundice in the UK is guided by the NICE guideline. Any infant with high serum bilirubin or a rapidly rising bilirubin level needs to be treated urgently to avoid neurotoxicity. High levels of conjugated bilirubin in a term baby can indicate biliary atresia, and babies with persisting jaundice must have their level of conjugated bilirubin measured. Preterm infants on long-term parenteral nutrition may develop conjugated jaundice which generally improves with the introduction of enteral feed and weaning of intravenous nutrition.

Neonatal hemolysis and risk of bilirubin-induced neurologic dysfunction

The pathologic phenotype of severe hyperbilirubinemia in the newborn infant is primarily due to excessive bilirubin production and/or impaired conjugation, resulting in an increased bilirubin load. This may, in turn, increase an infant's risk for the development of bilirubin-induced neurologic dysfunction (BIND). The highest-risk infants are those with increased bilirubin production rates due to hemolysis. Several immune and non-immune conditions have been found to cause severe hemolysis, and these are often exacerbated in those infants with perinatal sepsis and genetic predispositions. Therefore, identification of these infants, with novel technologies, is paramount in reducing the incidence of BIND and the long-term neurologic sequelae for these at-risk infants.

Hyperbilirubinemia, hemolysis, and increased bilirubin neurotoxicity

Increased hemolysis in the presence of severe neonatal hyperbilirubinemia appears to augment the risk of bilirubin neurotoxicity. The mechanism of this intensifying effect is uncertain. In direct antiglobulin titer (DAT) positive, isoimmune hemolytic disease, the bilirubin threshold at which neurotoxicity occurs appears to be lower than in DAT-negative hyperbilirubinemia. In other hemolytic conditions, the hemolysis may simply facilitate the development of extremely high serum bilirubin levels. Whether the hemolytic process per se exerts an independent effect or whether a very rapid rise in serum bilirubin might lead to greater penetration of the blood-brain barrier is unclear. In this review, we survey the synergistic role of hemolysis associated with severe hyperbilirubinemia in the potentiation of bilirubin-induced neurotoxicity and suggest methods of identifying at-risk babies with increased hemolysis to allow for their increased surveillance.

End-tidal carbon monoxide and hemolysis

Hemolytic disease in newborns can result from a number of conditions, which can place such infants at an increased risk for the development of severe hyperbilirubinemia. Because the catabolism of heme produces equimolar amounts of carbon monoxide (CO) and bilirubin, measurements of end-tidal breath CO (corrected for ambient CO) or ETCOc can serve as an index of hemolysis as well as of bilirubin production from any cause. Elevated levels of ETCOc have been correlated with blood carboxyhemoglobin levels and thus hemolysis. However, the detection of hemolysis can be a clinically challenging problem in newborns. Here, we describe the importance of determining ETCOc levels and their application in identifying infants at risk for developing hyperbilirubinemia associated with hemolysis and other causes of increased bilirubin production.

The contribution of hemolysis to early jaundice in normal newborns

OBJECTIVE

Neonatal jaundice is the result of an imbalance between bilirubin production and elimination, and our objective was to clarify the contribution of an increase in bilirubin production to hyperbilirubinemia in newborns.

METHODS

We measured the end-tidal carbon monoxide concentration corrected for ambient carbon monoxide concentration in 108 jaundiced newborns (total serum bilirubin level >75th percentile) and 164 control newborns in our well-infant nursery, for the first 4 days after birth.

RESULTS

Mean end-tidal carbon monoxide levels decreased in the control infants in the first 4 days but increased in the hyperbilirubinemic group. The differences between the jaundiced and nonjaundiced infants were statistically significant on all days.

CONCLUSIONS

Before hospital discharge, most infants with bilirubin levels >75th percentile are producing significantly more bilirubin than those with lower bilirubin levels. Because the ability of newborns to conjugate bilirubin is significantly impaired in the first few days, even a small increase in the rate of production can contribute to the development of hyperbilirubinemia. These data suggest that increased heme catabolism is an important mechanism responsible for hyperbilirubinemia in the first 4 days after birth.

Management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation

Jaundice occurs in most newborn infants. Most jaundice is benign, but because of the potential toxicity of bilirubin, newborn infants must be monitored to identify those who might develop severe hyperbilirubinemia and, in rare cases, acute bilirubin encephalopathy or kernicterus. The focus of this guideline is to reduce the incidence of severe hyperbilirubinemia and bilirubin encephalopathy while minimizing the risks of unintended harm such as maternal anxiety, decreased breastfeeding, and unnecessary costs or treatment. Although kernicterus should almost always be preventable, cases continue to occur. These guidelines provide a framework for the prevention and management of hyperbilirubinemia in newborn infants of 35 or more weeks of gestation. In every infant, we recommend that clinicians 1) promote and support successful breastfeeding; 2) perform a systematic assessment before discharge for the risk of severe hyperbilirubinemia; 3) provide early and focused follow-up based on the risk assessment; and 4) when indicated, treat newborns with phototherapy or exchange transfusion to prevent the development of severe hyperbilirubinemia and, possibly, bilirubin encephalopathy (kernicterus).

Infants with bilirubin levels of 30 mg/dL or more in a large managed care organization

OBJECTIVE

To describe the incidence, etiology, treatment, and outcome of newborns with total serum bilirubin (TSB) levels >or=30 mg/dL (513 micro mol/L).

DESIGN

Population-based case series.

SETTING

Eleven Northern California Kaiser Permanente Medical Care Program hospitals and 1 affiliated hospital.

PATIENTS

Eleven infants with TSB levels of >or=30 mg/dL in the first 30 days after birth, identified using computer databases from a cohort of 111,009 infants born 1995-1998.

OUTCOME MEASURES

Clinical data from the birth hospitalization, rehospitalization, and outpatient visits in all infants; psychometric testing at age 5 (N = 3), neurologic examinations by child neurologists at age 5 (N = 3), or primary care providers (N = 7; mean age: 2.2 years); Parent Evaluation of Developmental Status (N = 8; mean age: 4.2 years).

RESULTS

Maximum TSB levels of the 11 infants ranged from 30.7 to 45.5 mg/dL (525 micro mol/L to 778 micro mol/L; mean: 34.9 mg/dL [597 micro mol/L]). Four were born at 35 to 36 weeks gestation, and 7 were exclusively breastfed. Two had apparent isoimmunization; the etiology for the other 9 remained obscure, although only 4 were tested for glucose-6-phosphate dehydrogenase deficiency and 1 was bacteremic. None had acute neurologic symptoms. All received phototherapy and 5 received exchange transfusions. One infant died of sudden infant death syndrome; there was no kernicterus at autopsy. Two were lost to follow-up but were neurologically normal when last seen for checkups at 18 and 43 months. One child was receiving speech therapy at age 3. There were no significant parental concerns or abnormalities in the other children.

CONCLUSIONS

In this setting, TSB levels >or=30 mg/dL were rare and generally unaccompanied by acute symptoms. Although we did not observe serious neurodevelopmental sequelae in this small sample, additional studies are required to quantify the known, significant risk of kernicterus in infants with very high TSB levels.

Evaluation of the direct antiglobulin (Coombs') test for identifying newborns at risk for hemolysis as determined by end-tidal carbon monoxide concentration (ETCOc); and comparison of the Coombs' test with ETCOc for detecting significant jaundice

OBJECTIVE

First, to determine the sensitivity, specificity, and positive predictive value (PPV) of the direct antiglobulin test (DAT) for significant hemolysis in the neonate, as referenced to end-tidal carbon monoxide, the criterion standard for estimating the rate of hemolysis; and second, to evaluate the predictive value of the two procedures for significant jaundice.

DESIGN

Consecutive term newborns admitted to the nursery of an inner-city university hospital over a 15-week period. DAT screening by the Blood Bank was performed on all. End-tidal carbon monoxide levels were obtained at 12+/-6 and at 24+/-6 hours of age. Infants of nonsmoking mothers whose 12-hour exhaled carbon monoxide level was > or = 95th percentile were defined as having significant hemolysis.

RESULTS

n=660; DAT was positive in 23 (3.5%). Using the 12-hour end-tidal carbon monoxide > or = 3.2 microl/l (> or = 95th percentile) as reference (n=499 nonsmokers), the sensitivity of the DAT was 38.5% (10 of 26) and specificity 98.5% (466 of 473) for the detection of significant hemolysis. The PPV of the DAT for significant hemolysis at 12 hours was 58.8% (10 of 17). For significant jaundice the PPV of end-tidal carbon monoxide was greater than that for DAT (65.4% vs 52.9%), although not statistically so (p=0.25). The negative predictive values were similar.

CONCLUSION

DAT fails to identify over half of the cases of significant hemolysis that are diagnosed by end-tidal carbon monoxide. A neonate with a positive DAT has about a 59% chance of having significant hemolysis. End-tidal carbon monoxide may also provide a more sensitive index for predicting significant jaundice.

Low glucose-6-phosphate dehydrogenase enzyme activity level at the time of hemolysis in a male neonate with the African type of deficiency

Glucose-6-phosphate dehydrogenase (G6PD) levels are not usually drawn in the evaluation of black neonates with hyperbilirubinemia because of the oft-stated opinion that the levels may be normal at the time of hemolysis and thus will be misleading. In fact, this opinion is not applicable to newborns as many studies have shown that deficiency in the conjugating ability of the liver, not hemolysis, is the main cause of neonatal jaundice associated with G6PD deficiency. We present a case report of a neonate with brisk hemolysis and hyperbilirubinemia in whom the G6PD level was abnormally low at the time of the hemolytic episode. DNA analysis showed him to have the A-(202A,376G) variant and, as well, the UGT1A1 promoter repeat polymorphism associated with Gilbert's disease. This case, as well as a review of the literature, indicates that enzyme levels are not normal in patients with G6PD A- who are undergoing hemolysis.

Clinical rounds in the well-baby nursery: treating jaundiced newborns

Ten pearls (and pitfalls) in the management of the jaundiced newborn: Remember to take a history. Ask about jaundice in previous siblings and check family ethnicity. Don't ignore jaundice in the first 24 hours--it is considered pathologic until proven otherwise. Some normal infants may appear jaundiced and have a bilirubin level of 5 mg/dL at 23 hours and 59 minutes. On the other hand, a bilirubin level of 5 mg/dL at 10 hours is almost certainly pathologic. Use your judgment. Don't treat 35 to 37 week gestation infants as if they were full-term infants. Although these babies are cared for in well-baby nurseries and are generally treated like full-term infants, they are not full term. They are not as vigorous and do not nurse as well as full-term infants. Infants at 37 weeks gestation are four times more likely to have a serum bilirubin level greater than 13 mg/dL than those at 40 weeks gestation. Don't send 35-week gestation infants home before 48 hours. Document your assessment, particularly if the infant is being discharged early. Document the presence or absence of jaundice and its severity. A late rising bilirubin is typical of G6PD deficiency. Think about the ethnic background: G6PD deficiency is much more likely to occur in families from Greece, Turkey, Sardinia, and Nigeria, and particularly in Sephardic Jews from Iraq, Iran, Syria, and Kurdistan. Your practice may not contain many such families but remember in today's world of travel and intermarriage, etc, these genes are ubiquitous and the diagnosis of G6PD deficiency should always be considered in a newborn child with a significant elevation of bilirubin, particularly if it is a male and the rise in bilirubin is of late onset. Don't use homeopathic doses of phototherapy. As with any drug, phototherapy should be provided in a therapeutic dose (see above), but with the light sources commonly used, it is impossible to overdose the patient. Don't ignore a failure of response to phototherapy. If the bilirubin rises despite adequate phototherapy, there must be a reason. Consider the possibility of an unrecognized hemolytic process. Provide timely follow-up. Infants discharged (as most are) before 48 hours should be seen by a health-care professional within 2 to 3 days of discharge. Don't ignore prolonged jaundice. About one in three normal breast-fed infants still will be clinically jaundiced when they are 2 weeks old (two thirds will be biochemically jaundiced). These infants all have indirect hyperbilirubinemia. Occasionally, however, an infant with prolonged jaundice has direct hyperbilirubinemia. In these infants, the diagnosis of biliary atresia or some other cause of cholestatic jaundice must be considered. If the infant is clinically jaundiced beyond age 2 weeks, you should: 1) check the newborn record to make sure that the metabolic screen for hypothyroidism is normal (congenital hypothyroidism is a cause of indirect hyperbilirubinemia), and 2) ask the mother about the color of the urine and stool. If the baby's stools are pale or the urine is dark yellow, you must get a direct bilirubin to rule out cholestasis. If there is direct hyperbilirubinemia, a urine dipstick will identify the presence of bile (bilirubin). If the color of the urine and stool are normal (by history), it is reasonable to follow the child for another week. However, any infant who is still jaundiced beyond age 3 weeks must have a measurement of direct bilirubin. Don't ignore severe jaundice. If the bilirubin is sufficiently elevated, kernicterus can occur in a healthy, breast-fed infant.