A 48-hour-old male neonate is evaluated in the nursery for worsening jaundice. He was born… — USMLE Step 2 CK

A $48$ -hour-old male neonate is evaluated in the nursery for worsening jaundice. He was born at $39$ weeks of gestation via spontaneous vaginal delivery to a $26$ -year-old primigravid mother. His birth weight was $3400\text{ g}$ . APGAR scores were $8$ and $9$ at $1$ and $5$ minutes, respectively. The mother's blood type is O, Rh-positive, and the infant's blood type is A, Rh-positive. The direct antiglobulin test (Coombs test) is positive. The infant is exclusively breastfed and latching well.

Vital signs are:
Temperature: $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ )
Heart rate: $138\text{/min}$
Respiratory rate: $38\text{/min}$
Blood pressure: $68/42\text{ mmHg}$
Oxygen saturation: $99\%$ on room air

Physical examination reveals marked scleral icterus and jaundice extending to the lower abdomen. The infant is alert and active with normal tone. Additionally, there is a prominent, blotchy erythematous rash with scattered $1\text{-to-}2\text{ mm}$ pale-yellow pustules over the trunk and proximal extremities.

Laboratory studies show:

Laboratory Test	Result
Hemoglobin	$13.2\text{ g/dL}$
Reticulocyte count	$7.5\%$
Total bilirubin	$16.5\text{ mg/dL}$
Direct bilirubin	$0.6\text{ mg/dL}$

Which of the following is the most appropriate next step in the management of this patient?

Initiation of phototherapy and routine skin careCevap
B
Initiation of phototherapy and intravenous acyclovir
C
Immediate double-volume exchange transfusion
D
Intravenous administration of ampicillin and gentamicin
E
Reassurance and repeat serum bilirubin measurement in 24 hours

Cevap

Initiation of phototherapy and routine skin care

The correct management is the initiation of phototherapy and routine skin care. This neonate presents with pathological unconjugated hyperbilirubinemia caused by ABO hemolytic disease (indicated by the O/A blood type mismatch, positive direct antiglobulin test, and elevated reticulocytes). Because hemolysis is a recognized risk factor for bilirubin neurotoxicity, this patient is evaluated using high-risk treatment thresholds. At 48 hours of life, a total serum bilirubin of

16.5\text{ mg/dL}

is well above the threshold for phototherapy (typically around

11-13\text{ mg/dL}

for this risk group), necessitating immediate treatment to prevent acute bilirubin encephalopathy and kernicterus. However, the bilirubin level has not yet reached the threshold for exchange transfusion (typically

\geq 18-19\text{ mg/dL}

). Concurrently, the infant has a prominent, blotchy erythematous rash with central pustules, which is the classic presentation of erythema toxicum neonatorum (ETN). ETN is a benign, self-resolving idiopathic rash seen in up to half of all full-term neonates within the first few days of life. The infant appears well and lacks any systemic signs of infection. Therefore, the rash requires only routine skin care alongside the targeted phototherapy.

Adım Adım Çözüm

Evaluate the underlying cause and severity of the infant's hyperbilirubinemia.

The infant has pathological unconjugated hyperbilirubinemia secondary to ABO hemolytic disease, with a total bilirubin of 16.5 mg/dL at 48 hours of life.

The maternal-fetal blood type mismatch (O+ mother, A+ infant), positive direct antiglobulin test, and elevated reticulocyte count confirm isoimmune hemolysis. This places the infant in a high-risk category for bilirubin neurotoxicity.

Determine the appropriate intervention for the bilirubin level based on established nomograms.

Phototherapy is strongly indicated, but exchange transfusion is not yet required.

At 48 hours of life in a high-risk infant, the threshold for phototherapy is approximately 11-13 mg/dL, which this patient exceeds. The threshold for exchange transfusion is approximately 18-19 mg/dL, which has not been reached.

Diagnose the infant's dermatologic presentation to guide skin care management.

The rash is diagnosed as erythema toxicum neonatorum (ETN), which is completely benign.

A blotchy erythematous rash with scattered pale-yellow pustules appearing in the first few days of life in an otherwise well-appearing, afebrile term neonate is the classic presentation of ETN. It requires no antibiotic or antiviral treatment, only routine care.

Anahtar Kavram

Neonatal hyperbilirubinemia thresholds and benign neonatal dermatoses

Tahmini Süre:1m 30s

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