KERNICTERUS LAB STUDIES
Category: Child Health
Abstract : kernicterus Lab Studies: • Hematologic studies: Hematologic laboratory evaluation is the cornerstone of evaluation of the baby with hyperbilirubinemia. Although jaundice can be appreciated clinically, observation alone is not a reliable method to assess the severity or estimate risk factors for the infant. • Total and direct bilirubin: Quantitative measurement of total
kernicterus Lab Studies:
• Hematologic studies:
Hematologic laboratory evaluation is the cornerstone of evaluation of the baby with hyperbilirubinemia. Although jaundice can be appreciated clinically, observation alone is not a reliable method to assess the severity or estimate risk factors for the infant.
• Total and direct bilirubin:
Quantitative measurement of total and direct bilirubin should be undertaken in every baby at risk for significant hyperbilirubinemia or kernicterus. Total bilirubin measures the aggregate of all forms of bilirubin in the serum. The direct fraction measures the amount of conjugated bilirubin. Subtraction of the direct fraction from the total yields the calculated indirect bilirubin, or the unconjugated form. Remember that the indirect fraction is composed of bound bilirubin, free bilirubin, and lumirubin if the baby is under phototherapy. Only the free bilirubin is available to cross the blood-brain barrier and has the potential to cause neurotoxicity. Attempts to measure the amount of bound albumin or to estimate the bound fraction from measures of serum albumin have not proved to be clinically useful.
o Serial measurements may be necessary to track the evolution of hyperbilirubinemia; frequency of measurements depends on the baby's gestational age, chronologic age, risk factors, and other clinical characteristics.
o Every baby with hyperbilirubinemia should have a direct fraction measured at least once to rule out direct hyperbilirubinemia. Direct hyperbilirubinemia in the neonate is defined as a direct fraction greater than one third of total bilirubin and is always pathologic. Subsequently, if the hyperbilirubinemia is established as the indirect type, obtaining a direct fraction with every measurement is unnecessary unless the hyperbilirubinemia develops after the expected time frame for typical neonatal hyperbilirubinemia.
o With the advent of early discharge (before the physiologic peak of serum bilirubin) some clinicians are advocating universal bilirubin measurements in all babies prior to discharge. Nomograms have been published that estimate a baby's risk of disease based on measured levels of bilirubin. The most recently published nomogram uses an hour-specific approach to address the difficulties posed by babies leaving the hospital within 24-48 hours of birth.
• Blood type:
The baby's blood type should be determined and compared with that of the mother. Mothers with blood type O may have circulating antibodies to other red cell antigens that can cross the placenta and cause hemolytic disease in a baby with a different blood type, such as blood type A or B. Similarly, mothers who are Rh negative may have antibody to the Rh antigen if they have not been treated with RhoGAM. Antibody to the Rh antigen causes the most fulminant type of hemolytic hyperbilirubinemia, termed erythroblastosis fetalis in its most severe form. ABO incompatibility can cause significant hemolysis as well. Minor antigens on the baby's RBC are also susceptible to immune-mediated hemolysis from maternally acquired antibody but usually to a lesser extent than the major antigens.
• Reticulocyte count:
Babies typically have reticulocyte counts higher than older infants and adults. However, significant elevation in the neonate's reticulocyte count (>7 mg/dL) can indicate the presence of an ongoing hemolytic process.
• Direct Coombs test:
This test assays for antibody on the RBC membrane. A positive result indicates that antibodies are attached to the RBC, placing it at risk for immune-mediated destruction. This is a qualitative test, so a positive result does not suggest the amount of antibody or the degree of hemolysis. (However, pairing these results with the reticulocyte count can provide some idea of the severity of the process.) This test, although reliable, does not have 100% sensitivity. Because false-negative results do occur, repeating a test with an initial negative result is not unreasonable if the clinical course supports an ongoing hemolytic process.
• Complete blood cell count:
A CBC with manual differential should always be included in the evaluation of a jaundiced newborn. Measurement of the hemoglobin and hematocrit can be helpful to determine if ongoing hemolysis severe enough to cause anemia is present. The peripheral smear inspection is particularly valuable because it may reveal large amounts of nucleated RBCs, suggesting active reticulocytosis; it may show abnormally shaped RBCs in the case of hereditary membrane defects such as spherocytosis and elliptocytosis or marked ovalocytosis in the case of hemolytic disease of the newborn. Babies with sepsis can develop hyperbilirubinemia, and, although not conclusive, normal total white blood cell count and manual differential can be reassuring in a healthy-appearing baby with hyperbilirubinemia.
• Serum electrolytes:
Breastfed babies are known to normally develop higher levels of serum bilirubin than their formula-fed counterparts. However, with the trend toward earlier discharge, most breastfed babies are being discharged home before breastfeeding is well established, and a concomitant increase has occurred in the number of babies admitted in the first week of life with hypernatremic dehydration. Many of these babies are also significantly hyperbilirubinemic, and the resurgence of kernicterus from its previous virtual obsolescence is being attributed partly to this situation. Therefore, assessing serum sodium, potassium, chloride, bicarbonate, BUN, and creatinine levels is essential; initiate treatment as appropriate
• Lumbar puncture:
In the initial evaluation of hyperbilirubinemia, sepsis may be included in the differential diagnosis. If so, collection of spinal fluid for culture and cell count is essential to rule out meningitis. If the baby is having neurologic symptoms, cerebral spinal fluid (CSF) evaluation is imperative; depending on the baby's symptoms, expanding the evaluation beyond the normal aerobic bacterial culture may be prudent. If, on the other hand, the baby is vigorous and well-appearing with isolated hyperbilirubinemia as the only symptom, a spinal tap may not be necessary.
Hit: 331 times
Related Articles in Child Health :
|
Advertise with Health Information Encyclopedia