A 23-hour-old girl is evaluated for jaundice in the newborn nursery. The infant was born at term via cesarean delivery to a 33-year-old mother, gravida 2 para 2. The pregnancy was complicated by systemic lupus erythematosus and end-stage renal disease, for which the mother received regular hemodialysis. The delivery was complicated by intraamniotic infection and arrest of labor, necessitating cesarean delivery. Apgar scores were 8 and 9 at 1 and 5 minutes, respectively. The infant was prescribed ampicillin and cefotaxime shortly after delivery. The patient is exclusively breastfeeding and has lost 3% of her body weight. She has urinated twice and stooled once. Physical examination shows jaundice on the face and upper trunk but is otherwise unremarkable. Laboratory results are as follows: Which of the following is the most likely explanation for this patient's elevated creatinine level?

Question

A 23-hour-old girl is evaluated for jaundice in the newborn nursery.  The infant was born at term via cesarean delivery to a 33-year-old mother, gravida 2 para 2.  The pregnancy was complicated by systemic lupus erythematosus and end-stage renal disease, for which the mother received regular hemodialysis.  The delivery was complicated by intraamniotic infection and arrest of labor, necessitating cesarean delivery.  Apgar scores were 8 and 9 at 1 and 5 minutes, respectively.  The infant was prescribed ampicillin and cefotaxime shortly after delivery.  The patient is exclusively breastfeeding and has lost 3% of her body weight.  She has urinated twice and stooled once.  Physical examination shows jaundice on the face and upper trunk but is otherwise unremarkable.  Laboratory results are as follows:  Which of the following is the most likely explanation for this patient's elevated creatinine level?

Quizplus · Accepted Answer

A serum creatinine level is an effective marker of kidney disease in adults; however, in neonates, the creatinine level is often a reflection of the maternal level because creatinine freely crosses the placenta. In healthy term infants, creatinine levels decrease rapidly over the first 2 postnatal weeks to a nadir reflective of infant muscle mass. Therefore, a creatinine level is often a suboptimal determinate of kidney disease; however, these levels are often drawn as part of the sepsis workup, such as in this neonate, and require additional evaluation. In these cases, the first step in evaluation includes assessment of oliguria (normal urine output is at least one void per day of life), edema, and hypertension, which would suggest renal disease. Patients with any of these signs require possible renal ultrasound and additional laboratory evaluation (eg, trending serum creatinine), particularly if there are risk factors for renal injury (eg, nephrotoxic medications, perinatal hypoxia). This neonate's normal urine output and unremarkable physical examination (eg, normotensive, expected weight loss) suggest normal kidneys. Therefore, the serum creatinine level is reflective of the mother's creatinine level from renal failure. (Choice A) In cases of bilateral renal agenesis, serum creatinine rises abnormally after birth; however, no or minimal urine output is expected (this patient has voided twice). In addition, patients typically have respiratory distress (secondary to pulmonary hypoplasia) and other findings of Potter sequence (eg, flat nose, limb deformities). (Choices B and C) Breastfeeding jaundice occurs due to inadequate fluid intake while breastfeeding is being established and often indicates relative dehydration, which can lead to prerenal, acute kidney injury. Although this patient has mild jaundice, there is no evidence of dehydration (eg, adequate urine output, expected weight loss from birthweight [<10%]), and bilirubin is normal for age. (Choice D) Hypoxic-ischemic renal injury results from a perinatal insult, leading to an abnormally elevated serum creatinine; however, this infant's normal Apgar scores (8 and 9) and examination make perinatal asphyxia unlikely. Educational objective: Serum creatinine at birth is equivalent to the serum creatinine of the mother because creatinine passes across the placenta. In healthy term infants, creatinine normalizes over the first 2 weeks of life to a nadir that reflects neonatal muscle mass. References: Neonatal acute kidney injury. (http://www.ncbi.nlm.nih.gov/pubmed/26169430)

A 23-Hour-Old Girl Is Evaluated for Jaundice in the Newborn