• If donor blood of one blood type is transfused into a recipient with a different blood type, a transfusion reaction is likely to occur.
• In this reaction, the donor RBCs are agglutinated.
• It is rare for the transfused blood to cause agglutination of the recipient’s RBCs.
• This is because the donor plasma is rapidly diluted by the large amount of the recipient’s plasma.
• Dilution lowers the titer of the donor agglutinins to a level that is usually too low to cause agglutination.
• The small amount of transfused blood does not significantly dilute the recipient’s plasma agglutinins.
• Therefore, the recipient’s agglutinins can still agglutinate the mismatched donor RBCs.
• As explained earlier, all transfusion reactions eventually cause:
  • Immediate hemolysis due to hemolysins, or
  • Delayed hemolysis due to phagocytosis of agglutinated RBCs.
• Hemoglobin released from destroyed RBCs is converted into bilirubin by phagocytes.
• The bilirubin is later excreted in the bile by the liver.
• The bilirubin level in body fluids may rise enough to cause jaundice.
• In jaundice, the internal tissues and skin become yellow because of bile pigment.
• If liver function is normal, the bilirubin is excreted into the intestines through bile.
• Therefore, jaundice usually does not develop in adults unless more than 400 mL of blood is hemolyzed within less than one day.

Key Concept

• Mismatched blood transfusion mainly causes agglutination of donor RBCs by the recipient’s agglutinins.
• Donor agglutinins are greatly diluted in the recipient’s plasma and usually do not agglutinate the recipient’s RBCs.
• Transfusion reactions cause immediate or delayed hemolysis.
• Released hemoglobin is converted into bilirubin, which may cause jaundice.
• In adults with a normal liver, jaundice usually appears only when more than 400 mL of blood is hemolyzed in less than one day.

Acute Kidney Failure After Transfusion Reactions

• One of the most serious complications of a transfusion reaction is acute kidney injury.
• It can begin within a few minutes to a few hours after the transfusion.
• It may continue until the person dies from acute renal failure.
• There are three main causes of kidney shutdown:
• 1. Renal vasoconstriction
  • The antigen–antibody reaction releases toxic substances from the hemolyzed blood.
  • These toxic substances cause powerful constriction of the renal blood vessels (renal vasoconstriction).
• 2. Decreased arterial pressure
  • Loss of circulating RBCs and the production of toxic substances from hemolyzed cells, along with the immune reaction, can cause circulatory shock.
  • Arterial blood pressure falls.
  • Renal blood flow decreases.
  • Urine output decreases.
• 3. Blockage of renal tubules by precipitated hemoglobin
  • Large amounts of free hemoglobin are released into the blood after hemolysis.
  • If the amount of free hemoglobin is greater than the binding capacity of haptoglobin, excess hemoglobin remains free.
  • Haptoglobin is a plasma protein that binds small amounts of hemoglobin.
  • Excess free hemoglobin passes through the glomerular membrane into the kidney tubules.
  • If only a small amount enters the tubules, it is reabsorbed into the blood through the tubular epithelium.
  • If a large amount enters the tubules, only a small portion is reabsorbed.
  • Water continues to be reabsorbed.
  • This increases the hemoglobin concentration inside the tubules.
  • The hemoglobin precipitates.
  • The precipitated hemoglobin blocks many kidney tubules.
• Together, renal vasoconstriction, circulatory shock, and renal tubular blockage cause acute renal shutdown.
• If the kidney shutdown is complete and does not recover, the patient usually dies within 7 to 12 days unless treated with an artificial kidney.

Key Concept

• Acute kidney injury is one of the most dangerous complications of a transfusion reaction.
• Three main causes:
  • Renal vasoconstriction
  • Decreased arterial pressure (circulatory shock)
  • Blockage of renal tubules by precipitated hemoglobin
• These three mechanisms lead to acute renal shutdown.
• Without recovery or treatment with an artificial kidney, death may occur within 7–12 days.