What is the most likely cause of jaundice in a 7-day-old infant who is breastfed but appears undernourished?

The most likely cause of jaundice in a 7-day-old infant who is breastfed but appears undernourished is breastfeeding jaundice. This condition typically arises when an infant does not receive adequate milk intake, which can result from insufficient breastfeeding frequency or an ineffective latch. When a breastfeeding infant is undernourished, there may not be enough caloric intake, leading to dehydration and insufficient urine output, which can cause hyperbilirubinemia.

Breastfeeding jaundice occurs typically in the first week of life due to inadequate breastfeeding or low calorie intake, resulting in higher bilirubin levels in the blood. The bilirubin is a byproduct of the normal breakdown of red blood cells and is usually processed by the liver. If the intake is inadequate, bilirubin levels can rise, resulting in jaundice.

In contrast, other potential causes of jaundice, such as hemolytic disease, infection, or metabolic disorders, have different presentations or can be ruled out based on additional clinical findings. Hemolytic disease would usually present with more severe jaundice and signs of anemia shortly after birth. Infection would typically show associated symptoms such as fever or lethargy, and metabolic disorders often have other systemic signs present at birth.

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