If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 3 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
This month’s stumper
A 30-hour-old newborn born full-term via vaginal delivery to a healthy 28-year-old mother appears slightly yellow. There were no complications at delivery and the baby has been feeding well. A bilirubin level returns at 18 mg/dL with direct bilirubin at 0.6 mg/dL. The parents are now concerned about the baby's discoloration.
Which of the following is the next step in management?
A. Reassure mother that this is completely normal and no additional studies or treatment are indicated.
B. Repeat bilirubin level immediately as the result must be a lab error.
C. Start phototherapy and repeat bilirubin level in six hours.
D. Transfer patient to nearest neonatal intensive care unit for an exchange transfusion.
E. Wait six hours and repeat bilirubin level.
The correct answer is C.
Kaplan Medical explains why
Jaundice is a common occurrence in the first week of life. "Physiologic jaundice" is usually transient and due to an increased bilirubin load from increased red blood cell volume, decreased survival time of the red blood cell, and increased enterohepatic circulation. Other factors include defective hepatic uptake of bilirubin and inadequate conjugation of bilirubin to bilirubin glucuronide for excretion.
Normal cord blood bilirubin level is about 1.5 mg/dL, and neonate serum bilirubin normally increases by maximum 5 mg/dL in 24 hours to maximum 15 mg/dL at three days of life. A level of 18 mg/dL at 30 hours of life is not normal and requires phototherapy. Phototherapy should bring the level down by 1–2 mg/dL within four to six hours. The level should be checked at that time to ensure it is dropping.
Besides phototherapy, one should investigate the cause for the rapid rise of bilirubin. The most important consideration is the blood type of the mother and of the infant. A direct Coombs test should also be performed. Other things to keep in mind include a red cell defect such as hemoglobinopathy, polycythemia, extravascular blood loss, bacterial sepsis, increased enterohepatic circulation (from an intestinal obstruction), disorder of bilirubin metabolism, or endocrine disorder such as hypothyroidism.
Why the other answers are wrong
Choice A: Reassurance that this is normal is incorrect. This baby needs to be treated for hyperbilirubinemia and more blood will need to be drawn to follow the levels. The mother should be reassured that this is a common occurrence, usually transient and without future implication on the baby's development if treated appropriately.
Choice B: Repeating the labs is not correct because although lab error is something to keep in mind when interpreting all test results, this baby is jaundiced and thus unlikely to have a normal bilirubin level. Jaundice usually becomes apparent at levels of 5 mg/dL in the neonate. As levels get higher, the jaundice usually progresses from the face to the trunk and then down the body.
Choice D: Exchange transfusion is not yet warranted in this baby. If the level were greater than 25 mg/dL or started at greater than 20 mg/dL and did not improve with phototherapy, this baby would require an exchange transfusion. During this procedure, blood is removed from the baby (usually from an umbilical artery catheter), and the baby is transfused with cross matched blood through a venous catheter. The exchange is done in 15 mL increments. There are multiple risks to the procedure, including thromboemboli, dysrhythmia, hyperkalemia, hypernatremia, DIC or transfusion reaction.
Choice E: Wait six hours and repeat is incorrect because the bilirubin level is too high for you to wait. If the bilirubin level is allowed to rise unchecked, the baby is put at risk for kernicterus. When the level of unconjugated bilirubin reaches higher than 20 mg/dL in a full-term neonate, it can become neurotoxic by accumulating in the basal ganglia, pons, or cerebellum-causing kernicterus. Clinically, it manifests as a variety of neurologic symptoms ranging from lethargy and hypotonia to severe encephalopathy and death. At the present rate of rise, the bilirubin is likely to be higher than 20 mg/dL in six hours.
Tips to remember
- Newborns with jaundice should have a bilirubin level drawn.
- Patients with a bilirubin level more than 15 mg/dL should undergo phototherapy.
- After phototherapy for six hours, bilirubin should be checked again to make sure that levels are decreasing.
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.
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