What are the signs and symptoms of ABO (Blood Type) incompatibility?

Signs and Symptoms of ABO Incompatibility

ABO incompatibility causes acute hemolytic reactions with hypotension, hemoglobinuria, and hemoglobinemia as the most frequent clinical findings, and the severity directly correlates with the volume of incompatible blood transfused. 1

Clinical Presentation Based on Volume Transfused

The clinical manifestations of ABO incompatibility vary dramatically based on the amount of incompatible blood administered:

High-Volume Transfusion (>50 mL)

• 64% of patients develop signs or symptoms when more than 50 mL of incompatible blood is transfused 1
• 17% mortality rate in this group 1
• Symptoms typically manifest during or shortly after transfusion 2

Low-Volume Transfusion (≤50 mL)

• Only 25% develop symptoms when 50 mL or less is transfused 1
• Zero mortality reported in this group 1
• Early recognition and discontinuation are critical to prevent progression 1

Cardinal Signs and Symptoms

Most Common Manifestations (in order of frequency)

• Hypotension - occurs in both survivors and fatal cases 1
• Hemoglobinuria (dark or red-colored urine from free hemoglobin) 1
• Hemoglobinemia (visible free hemoglobin in plasma) 1
• Severe febrile reactions during or immediately after transfusion 2

Additional Clinical Features

• Weight gain from fluid retention (with or without ascites) 2
• Tender hepatomegaly 2
• Jaundice 2
• Acute renal failure from hemoglobin precipitation in renal tubules 3
• Disseminated intravascular coagulation (DIC) in severe cases 3

Mechanism of Symptoms

ABO incompatibility triggers brisk complement-mediated intravascular hemolysis due to preformed IgM and IgG antibodies (isohemagglutinins) present in all individuals except group AB 3. This immediate immune response distinguishes ABO incompatibility from other transfusion reactions by its rapid onset and severity 3.

Special Population: Neonatal ABO Incompatibility

In hemolytic disease of the newborn from ABO incompatibility:

• Severe hyperbilirubinemia developing rapidly in the first 48 hours of life 4
• Positive direct antiglobulin test (DAT) at birth on cord blood 4
• Risk of bilirubin encephalopathy if untreated 4
• Most commonly occurs in group A or B infants born to group O mothers, especially those of African origin 4, 5
• Maternal IgG titers can reach 1024 or higher in severe cases 5
• May require exchange transfusion in rare severe cases 5

Critical Timing Considerations

• Symptoms typically occur during transfusion or within minutes to hours after administration 2, 1
• In neonates, bilirubin levels can increase very rapidly in the first 48 hours of life 4
• The 72-hour window is critical for detecting newly formed antibodies in recently transfused patients 6

Common Pitfalls to Avoid

• Do not assume absence of symptoms means safety - 36% of patients receiving >50 mL remain asymptomatic despite receiving incompatible blood 1
• Do not delay discontinuation - prompt recognition and stopping the transfusion minimizes morbidity and mortality 1
• Do not discharge neonates before 72 hours without proper risk assessment for hyperbilirubinemia 4
• Do not skip the bedside identity check - 62% of ABO-incompatible transfusions occur at the patient's bedside due to identification errors 1

Severity Spectrum

Clinical presentation ranges from:

• Asymptomatic (particularly with small volumes) 1
• Mild symptoms requiring only supportive care 4
• Severe multiorgan dysfunction with potential for death 2, 1

The volume of incompatible blood transfused is the single best predictor of whether symptoms will develop and their severity 1.