Blood Pigment Elevated During Rapid RBC Destruction

When destruction of RBC rapidly occurs, the concentration of which of the following is increased in the blood?

Correct Answer: Bilirubin

When RBCs are rapidly destroyed (hemolysis), bilirubin accumulates in the blood — this is the hallmark of hemolytic jaundice.

Pathway of Hemoglobin Breakdown

• RBC destruction (in spleen, liver, bone marrow) → Hemoglobin released → split into globin (protein) + heme (iron + porphyrin).
• Heme → Biliverdin (green pigment, via heme oxygenase) → Bilirubin (yellow pigment, via biliverdin reductase).
• Unconjugated (indirect) bilirubin travels in blood bound to albumin → enters liver → conjugated with glucuronic acid → conjugated (direct) bilirubin → excreted in bile → becomes urobilinogen in intestine → excreted in faeces as stercobilin (brown colour) or in urine as urobilin (yellow colour).

Clinical Significance

• Rapid RBC destruction → excessive bilirubin → jaundice (icterus): yellow discoloration of sclera, skin, and mucous membranes.
• Example: Babesiosis (tick fever) in cattle causes massive hemolysis → hemolytic icterus + red/port-wine coloured urine (hemoglobinuria).