Final answer:
An elevated serum blood bilirubin level typically refers to a concentration higher than the normal upper limit of 1 mg/100ml, with levels surpassing 2 mg/100ml causing jaundice.
Step-by-step explanation:
Elevated Serum Blood Bilirubin Level
An elevated serum blood bilirubin level is generally considered above the normal concentration, which is less than 1 mg/100ml (17.1 µmol/L).
When the serum bilirubin level exceeds this threshold, the condition is known as hyperbilirubinemia.
In jaundice or icterus, the bilirubin concentration reaches a point where blood cannot maintain solubility beyond 2 mg/100 ml, leading to its diffusion into tissues and resulting in a yellow discoloration.
In newborns, a specific form of hyperbilirubinemia known as unconjugated hyperbilirubinemia occurs when the enzyme UDP glucuronyl transferase is not fully developed, causing unconjugated bilirubin to accumulate.
High levels of unconjugated bilirubin, especially over 25 mg/100 ml, may lead to serious conditions such as kernicterus.
Other related disorders, such as Crigler-Najjar syndrome and Gilbert's disease, are characterized by defects in the metabolism and handling of bilirubin by the liver, often leading to significantly elevated bilirubin levels.