An infant's indirect (unconjugated) serum bilirubin level is 10 mg/dL. The exact definition of a physiologic range and management of indirect hyperbilirubinemia is complex and based on many factors, including gestational age (GA), postnatal age, birthweight, disease state, risk factors, degree of hydration, nutritional status, and ethnicity. Total serum bilirubin (TSB) is the sum of direct (conjugated) and indirect (unconjugated) and can be measured in the blood. The indirect bilirubin is calculated by subtracting the direct bilirubin from the total bilirubin. Transcutaneous bilirubin (TcB) is a measurement of total serum bilirubin from an instrument that uses reflectance measurements on the skin and correlates well with the laboratory TSB value.