Delayed hemolytic episodes due to anti-M

Area of Science:

• Transfusion Medicine
• Immunology
• Hematology

Background:

• Alloantibodies, particularly Kidd system antibodies, can cause delayed hemolytic transfusion reactions.
• The behavior of anti-M antibodies in post-transfusion hemolysis is less understood.

Observation:

• Three cases of delayed hemolytic reactions occurred 5-15 days post-transfusion.
• Direct antiglobulin tests were negative pre-transfusion but weakly positive post-transfusion.
• Anti-M antibodies were detected in post-transfusion samples, causing hemolysis of compatible red blood cells.

Findings:

• Newly synthesized anti-M antibodies can cause accelerated hemolysis of transfused red blood cells.
• Hemolysis was mild and often clinically unsuspected until subsequent transfusion requests.
• Anti-M antibodies may become undetectable weeks after the hemolytic event.

Implications:

• Anti-M should be considered in cases of delayed hemolytic transfusion reactions, even when initially undetectable.
• This finding expands the known spectrum of alloantibody behavior in transfusion medicine.
• Awareness of anti-M's potential for delayed hemolysis is crucial for patient safety.