Peripheral Blood Smear Review
New Sysmex XN hematology analyzers for determination of complete blood counts (CBC) and differential white blood cell counts offer some new features:
- White and nucleated red blood cell (NRBC) channel, all samples include the NRBC count
- White cell precursor (IG) channel
- Low white cell count mode with extended count that provides an accurate differential
- Dedicated channel for fluorescent platelet count for when platelet count is low
These technological advances have improved the performance of automated hematology analyzers far beyond the capabilities of microscopic manual differential counts. Manual inspection is routinely performed to confirm abnormal parameters that have been flagged by the hematology analyzer. Clinical laboratories set rigorous quantitative and qualitative criteria for each cell type. Typical criteria include:
A. Based on CBC
- WBC (x 103/dL) is <1.0 or >50.0
- Hgb (g/dL) is <6.0
- RBC (x 106/dL) is >8.6
- MCV (fL) is <70 or >105
- PLT (x 103/dL) is <100 or >999
- NRBC (%) is >5
B. Based on automated DIFF results
- Lymphocytes (x103/dL) are >5.0
- Monocytes (x103/dL) are >1.5
- Eosinophils (x103/dL) are >2.0
- Basophils (x103/dL) are >0.5
- IG (%) is >4.0
C. Qualitative Flags include an abnormal WBC scattergram, increased immature granulocytes (IG), presence of a left shift, atypical lymphocytes, blasts or NRBC.
The initial microscopic evaluation of all flagged specimens is performed by a clinical laboratory scientist. Their review serves several important functions including verification of automated results; identification of abnormal, immature and atypical cells; and recognition of clinically significant morphological abnormalities. Blood smear abnormalities identified on new patients or infrequent outpatient visitors are then submitted to a clinical pathologist for confirmation and further evaluation. Any comments and findings identified by the clinical pathologist are reported as free text within the finalized report.
In rare circumstances, a peripheral blood specimen may not generate any abnormal flags by the instrument. These mostly include qualitative abnormalities such as hematological malignancies (e.g. chronic and acute leukemias, myelo-proliferative neoplasm, and myelodysplasia), hereditary hemolytic disorders (hereditary spherocytosis), and presence of infectious agents (malaria and ehrlichia). A separate request for peripheral blood smear review by a clinical pathologist should be restricted to these disorders, if clinical suspicion is high.
