**Core Concept**
Hyperbilirubinemia in newborns is a condition characterized by elevated bilirubin levels, which can lead to kernicterus if left untreated. The primary goal of management is to assess the severity of jaundice and identify potential causes to prevent complications.

**Why the Correct Answer is Right**
To determine the severity of hyperbilirubinemia, it is essential to measure the total serum bilirubin (TSB) level. TSB reflects the overall bilirubin concentration in the blood and is a critical parameter for assessing the risk of kernicterus. This measurement helps clinicians decide the need for phototherapy, exchange transfusion, or other interventions. The American Academy of Pediatrics recommends serial TSB measurements to monitor the effectiveness of treatment and adjust the management plan accordingly.

**Why Each Wrong Option is Incorrect**
**Option A:** Hematocrit is a measure of red blood cell concentration, which is not directly related to bilirubin levels.
**Option B:** Albumin levels are important in assessing liver function, but they do not directly reflect the severity of hyperbilirubinemia.
**Option C:** Blood type is relevant in Rh incompatibility, but it is not a direct measure of bilirubin levels.

**Clinical Pearl / High-Yield Fact**
When managing hyperbilirubinemia, it is essential to remember that the American Academy of Pediatrics recommends a treatment plan based on the hour-specific serum bilirubin levels, which are age-dependent and take into account the risk of kernicterus.

**Correct Answer: D. Total serum bilirubin (TSB) level.