What is included in a peripheral smear?

What is Included in a Peripheral Smear Examination

A peripheral blood smear examination includes morphological assessment of red blood cells, white blood cells, and platelets, with evaluation of cell distribution patterns, maturity, and any abnormal features that may indicate hematologic disorders.

Core Components of Peripheral Smear Evaluation

Red Blood Cell (RBC) Assessment

• Cell morphology and distribution patterns including evaluation for Rouleaux formation (red cells appearing as stacks of coins), which suggests elevated serum proteins as seen in multiple myeloma 1
• RBC size, shape, and color abnormalities to identify anemia types and other hematologic disorders 2
• Presence of red blood cell fragments when hemolytic uremic syndrome (HUS) is suspected, particularly in patients with diagnosed E. coli O157 or other Shiga toxin-producing organisms 1

White Blood Cell (WBC) Assessment

• Differential count of WBC types including neutrophils, lymphocytes, monocytes, eosinophils, and basophils 1, 3
• Detection of circulating plasma cells with careful attention to both percentage and absolute count, as presence of ≥20% circulating plasma cells or absolute count >2×10⁹/L indicates plasma cell leukemia 1
• Identification of blasts or immature cells to detect acute leukemia or other myeloid neoplasms 1
• Monocyte morphology evaluation including assessment for dysgranulopoiesis, promonocytes, and neutrophil precursors in cases of persistent monocytosis 4
• Detection of morulae in monocytes which suggests ehrlichiosis infection 4

Platelet Assessment

• Platelet count estimation and morphology to evaluate for thrombocytopenia or thrombocytosis 1
• Platelet size and granularity to identify platelet disorders 3

Clinical Context for Peripheral Smear Review

When Peripheral Smear is Essential

• Confirmation after abnormal automated complete blood count results, as manual microscopy provides definitive morphological assessment 5
• Evaluation of bleeding disorders, anemia, infectious disorders, and suspected leukemia in emergency and acute care settings 3
• Detection of early manifestations of HUS with frequent monitoring when STEC infection is diagnosed 1
• Assessment of large granular lymphocytic disease when flow cytometry suggests this diagnosis 1

Specific Disease Indicators

• Multiple myeloma evaluation requires peripheral smear to identify Rouleaux formation and circulating plasma cells 1
• Myelodysplastic syndrome workup includes peripheral smear review to determine presence of dysplastic features and assess blast percentage 1, 4
• Chronic myelomonocytic leukemia (CMML) diagnosis requires peripheral smear showing persistent monocytosis with evaluation of monocyte morphology 4

Technical Considerations

Preparation and Examination Standards

• Blood smear must be properly prepared with adequate cell distribution for accurate morphological assessment 1, 5
• Examination requires highly trained staff as manual differential counting demands expertise in recognizing pathological variations 6
• Automated microscopy systems (such as Cellavision DM96) can provide preclassification with 92% accuracy but still require expert review for final interpretation 6

Integration with Other Diagnostic Tests

• Peripheral smear complements but does not replace complete blood count with differential, bone marrow examination, flow cytometry, and cytogenetic analysis 1
• Should be reviewed in conjunction with clinical history including age, sex, ethnicity, prior malignancies, cytotoxic therapy exposure, and family history of hematologic disorders 1
• Recent confounding factors such as growth factor therapy, transfusions, or medications should be considered when interpreting results 1

Common Pitfalls to Avoid

• Failing to distinguish between relative and absolute cell counts can lead to misdiagnosis, particularly in monocytosis evaluation 4
• Overlooking transient polyclonal plasma cells in non-malignant conditions such as severe sepsis, infectious mononucleosis, or serum sickness, which can mimic plasma cell leukemia 1
• Not performing peripheral smear when automated counts show abnormalities delays diagnosis of serious hematologic conditions 1
• Relying solely on automated systems without expert morphological review can miss critical diagnostic features 6