The test used to measure bilirubin levels in neonatal jaundice is Serum bilirubin. This is because bilirubin, a breakdown product of hemoglobin, accumulates in the blood during jaundice. Measuring serum bilirubin provides a direct and quantitative assessment of the total bilirubin concentration, which is critical for diagnosing the severity of jaundice and guiding treatment decisions. Urine bilirubin and stool urobilinogen are less reliable in neonates due to immature liver conjugation and excretion pathways, while blood glucose is unrelated to bilirubin metabolism. Thus, serum bilirubin measurement is the gold standard for evaluating neonatal jaundice.
Reference: Nelson Textbook of Pediatrics, Kliegman et al., 21st Edition.