You are called to evaluate a 4-day-old infant in the nursery for worsening jaundice. The patient is the first child of a 32-year-old mother, who had an uncomplicated full-term pregnancy and normal spontaneous vaginal delivery. The mother is otherwise healthy but has a sister who had her gallbladder removed as a child. The infant has been formula fed and has been eating and stooling normally. The total bilirubin level is 19.2 mg/dL, with a direct fraction of 0.3 mg/dL. On physical examination, the infant is jaundiced but
otherwise well, with no other significant physical findings. SELECT THE ONE BEST ANSWER
1. The differential diagnosis of the unconjugated hyperbilirubinemia in this child includes which of the following?
(A) biliary atresia
(B) alpha1-antitrypsin deficiency
(C) ABO blood type incompatibility
(D) Caroli syndrome
(E) Sickle cell anemia
Answer
C
Neonatal jaundice occurs in approximately twothirds of infants and is defined by bilirubin levels higher than 5 mg/dL. Bilirubin is generated as one of the products of the breakdown of hemoglobin and the conjugation of bilirubin to bilirubin glucuronide occurs in the liver.
Neonatal unconjugated hyperbilirubinemia is therefore the result of either increased bilirubin production or decreased conjugation.
Neonatal hemolytic anemias, with increased bilirubin production, can result in severely abnormal unconjugated hyperbilirubinemia levels in neonates.
Blood group mismatches because of ABO or Rh mismatches are common causes of neonatal hemolytic
anemia and unconjugated hyperbilirubinemia.
Other causes of unconjugated hyperbilirubinemia include hemolytic anemias because of red blood cell membrane or enzyme defects and increased red blood cell turnover associated with polycythemia, internal hemorrhages such as cephalohematomas or intraventricular hemorrhages. Decreased bilirubin conjugation as
a result of Crigler-Najjar or Gilbert syndromes also result in unconjugated hyperbilirubinemia. Biliary
atresia, α1-antitrypsin deficiency, and Caroli syndrome are all causes of neonatal conjugated hyperbilirubinemia
2. The laboratory evaluation of this infant’s hyperbilirubinemia should include all of the following except
(A) complete blood count with smear
(B) indirect and direct Coombs test
(C) prothrombin time (PT)/partial thromboplastin time (PTT)
(D) maternal blood type
(E) reticulocyte count
Answer
C
Evaluation for suspected neonatal hemolytic anemias should include evaluation of the complete blood
count along with indirect and direct Coombs tests and maternal and neonatal blood types. In the absence of
excessive bleeding or bruising, there is no indication for coagulation studies. The complete blood count will
reveal the degree of anemia, if any, and the peripheral smear will demonstrate the morphologic features of
the red blood cells that could suggest underlying etiologies.
The Coombs tests will evaluate whether or not there are antibodies that could be contributing to
autoimmune or alloimmune hemolysis. Neonatal and maternal blood types are needed to evaluate the possible presence of ABO and Rh incompatibility.
3. Which of the following combinations of parents’ blood types place an infant at highest risk for
hemolytic anemia?
(A) maternal Rh negative, paternal Rh negative, first child
(B) maternal Rh negative, paternal Rh positive,second child
(C) maternal type O, paternal type O, first child
(D) maternal type AB, paternal type B, second child
(E) maternal type AB, paternal type A, first child
Answer
(B)
Mothers with Rh negative blood type develop antibodies against the Rh antigen after exposure during
pregnancy to an Rh-positive fetus or after transfusion with Rh-positive blood. In the presence of an
Rh-positive fetus, the mother’s antibodies can cross the placenta and destroy fetal red blood cells, resulting in neonatal hemolytic anemia. Rh hemolytic disease can be prevented with high titer Rho(D) immune globulin treatment for Rh-negative mothers who have been exposed to Rh-positive infants.
Similarly, mothers with type O blood have antibodies against antigens for blood types A and B that can
react to and destroy fetal red blood cells with these blood type antigens. However, a fetus that also possesses type O blood will not be susceptible to hemolysis from these antibodies. A mother with
type AB blood has no antibodies to blood group antigens, and therefore the fetus is not exposed to
any anti-red blood cell antigen antibodies. Despite the presence of these antibodies, only 33% of infants
with ABO “mismatch” will have a positive direct Coombs test, and of those, only 20% will develop
jaundice from excessive hemolysis
4. The differential diagnosis of a neonate with hemolytic anemia includes all of the following except
(A) pyruvate kinase deficiency
(B) ABO incompatibility
(C) Crigler-Najjar syndrome
(D) hereditary spherocytosis
(E) Rh disease
answer
(C)
Crigler-Najjar syndrome is caused by the absence of glucuronyl transferase and results in severe indirect
hyperbilirubinemia. Pyruvate kinase and G6PD are both red blood cell enzymes that, when deficient, can
result in neonatal hemolytic anemia. Hereditary spherocytosis, as well as other syndromes with red blood
cell structural abnormalities, such as hereditary elliptocytosis and paroxysmal nocturnal hemoglobinuria,
can also result in neonatal hemolytic anemia.
A maternal-fetal blood type mismatch such as ABO incompatibility results in alloimmune hemolytic
anemia, with the mother’s antibodies reacting to and destroying the neonatal red blood cells.
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Q 2:
Anewborn has delayed passage of meconium stools and barium enema radiograph shows dilated proximal colon and small obstructed distal colon. What should be the next diagnostic test?
(A) abdominal CT-scan
(B) stool studies
(C) rectal suction biopsies
(D) sweat chloride testing
(E) chromosome analysis
Answer :
(C)
Congenital megacolon (Hirschsprung disease) is the result of congenital absence of ganglion cells in a segment of large bowel. Absentor deficient peristalsis in the affected segment results in functional obstruction. This causes constipation and distention of bowel proximal to the aganglionic area. It is this chronically
distended bowel that has led to the name megacolon. Severe cases present as neonatal intestinal obstruction.
Practically all normal, full-term born neonates pass meconium in the first 48 hours of life. Hirschprung disease should be considered in any full-term infant with delayed passage of stool. Rectal manometry
and rectal suction biosy are the easiest and most reliable indicators of Hirschprung disease.
