What automated blood count is most likely to be interfered with by the presence of extremely microcytic Red Blood Cells (RBCs), schistocytes, or cytoplasmic fragments in Microangiopathic Hemolytic Anemia (MAHA)?

Automated Platelet Count Interference in Microangiopathic Hemolytic Anemia

The presence of extremely microcytic RBCs, schistocytes, or cytoplasmic fragments will most likely interfere with the automated platelet count.

Mechanism of Interference

Automated blood cell analyzers typically use one of two primary methods to count platelets:

1. Impedance method (electrical resistance): Counts cells based on their size as they pass through an aperture
2. Optical method: Uses light scatter properties to identify and count cells

Why Platelet Counts Are Affected

• Extremely microcytic RBCs and schistocytes have size ranges that overlap with platelets (typically 2-20 μm³)
• Cytoplasmic fragments from leukemic cells can be misidentified as platelets due to similar size characteristics
• The impedance method particularly struggles to differentiate between platelets and similarly-sized cellular fragments 1

Evidence Supporting Platelet Count Interference

Research has demonstrated that various cellular fragments can cause significant platelet count interference:

• Cytoplasmic fragments of leukemic cells can lead to falsely elevated platelet counts that don't correlate with peripheral smear findings 1
• Fragmented RBCs (schistocytes) in microangiopathic hemolytic anemia can be misclassified as platelets by automated analyzers 2
• Case reports have documented significant discrepancies between automated and manual platelet counts in patients with MAHA 3

Clinical Implications

The consequences of inaccurate platelet counts in MAHA are significant:

• Underestimation of thrombocytopenia: May delay critical interventions like plasma exchange in TTP
• Overestimation of platelet count: Can lead to false reassurance in potentially life-threatening conditions
• Treatment decisions: Platelet transfusion decisions may be inappropriately made based on inaccurate counts

Verification Methods

When platelet count interference is suspected:

1. Peripheral blood smear review: Essential to visually confirm the presence of schistocytes and assess true platelet numbers
2. Immunological platelet counting: Using flow cytometry with fluorochrome-labeled antibodies against platelet markers (CD41/CD61) 1
3. Phase-contrast microscopy: Can provide more accurate manual platelet counts 4

Common Pitfalls

• Relying solely on automated counts in patients with known or suspected MAHA
• Failing to correlate automated counts with peripheral smear findings
• Not recognizing sudden, unexplained changes in platelet counts as potential analyzer errors 5

Conclusion

In cases of microangiopathic hemolytic anemia with extremely microcytic RBCs, schistocytes, or cytoplasmic fragments, the automated platelet count is the parameter most likely to be affected by interference. This can lead to significant clinical consequences if not properly identified and addressed through manual verification methods.