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Platelet cold agglutinins: a flow cytometric analysis
1St Michael's Hospital, Toronto, ON, Canada.
Transfusion Science
|June 3, 1999
Summary
A rare cold agglutinin caused pseudothrombocytopenia in a patient. Flow cytometry identified this platelet cold agglutinin as a low-titer IgM antibody targeting GPIIbIIIa, with normal platelet function observed.
Area of Science:
- Hematology
- Immunology
- Clinical Pathology
Background:
- Spontaneous EDTA-independent cold platelet agglutination is a rare cause of pseudothrombocytopenia.
- Automated cell counters can misinterpret platelet clumping as low platelet counts.
Observation:
- A 49-year-old woman presented with abnormal vaginal bleeding and observed platelet clumping in multiple anticoagulant tubes.
- Flow cytometry revealed patient serum agglutinated normal platelets at lower temperatures, with increased IgM and C3 on patient platelets after cold incubation.
Findings:
- The platelet cold agglutinin was characterized as a low-titer IgM antibody with minimal activity above 30°C.
- Competitive inhibition studies indicated the antibody binds to the GPIIbIIIa complex on platelets.
- Despite agglutination, patient platelet function remained normal, as assessed by activation markers and aggregation studies.
Implications:
- Flow cytometry can quantify and characterize platelet cold agglutinins.
- While generally asymptomatic, this condition may pose risks during hypothermic procedures like cardiac surgery.
- Accurate diagnosis is crucial to avoid misinterpretation as true thrombocytopenia.