Peripheral Smear

Examination of the Peripheral Blood Smear

  • Date: March 2025

  • Source: Heme | 1304

Benefits of Automation

  • Reduces time spent in CBC (Complete Blood Count) analysis.

  • Improves efficiency in:

    • Flow cytometry

    • Reflex testing

  • Cost savings from reduced tech time spent on slide reviews.

  • Slide reviews decreasing to 10-15%, as most analyses reveal abnormalities leading to doctors' orders for further investigation.

Great Automation: Why Conduct a Slide Review?

  • Despite automation, peripheral smears remain constant in significance.

  • Slide reviews have decreased in frequency (10-15%).

  • Key conditions requiring review include:

    • Anemia

    • Leukemias

    • Presence of parasites

    • Detection of toxic changes

    • Platelet issues (e.g., aggregations, satellitism)

Purpose of a Peripheral Smear

  • Evaluation of WBCs (White Blood Cells), RBCs (Red Blood Cells), and Platelets is mandatory even if only one element is flagged.

  • All laboratories follow established protocols (SOPs) that determine triggers for manual review based on:

    • Studies

    • Standards of practice

  • Reviews may be initiated by:

    • Abnormal findings by Medical Laborator Technologists (MLTs)

    • Physician requests in response to flagged results.

Performing a Manual Smear

  • Initial scanning under 10x or 20x:

    • Examine 8-10 fields for:

      • RBCs: Check deviations in size, shape, distribution, hemoglobin concentration, color, and inclusions.

      • WBCs: Assess differentiation and nuclear/cytoplasmic abnormalities and abnormal inclusions.

      • Platelets: Verify count, shape, size, and clumping.

Identifying Abnormalities

  • MLT needs to decide if findings are artifactual or pathological:

    • Refractile RBCs may indicate water contamination, not inclusions.

    • Echinocytes (crenated cells) may appear as artifacts if spiculation is consistent across thin portions of the smear.

Detailed Examination under Low Power Field (LPF) 10x

  • Assessment Goals:

    • Determine staining quality of the smear.

    • Ensure good cell distribution by scanning edges and center, checking for:

      • Clumping of cells

      • Presence of abnormal cells and fibrin strands.

    • Locate optimal areas for detailed examination and enumeration of cells:

      • RBCs should not touch; overlapping is unacceptable.

      • No presence of broken cells or precipitated stains.

      • Observe graduated central pallor for subtle changes.

High Power (40x) Examination

  • WBC Estimate Procedure:

    • Average counts over 10 fields:

      • Example calculations: 4, 5, 5, 6, 4, 5, 4, 5, 6, 7 gives an average of 5.1 x 10^9/L.

    • Record morphological abnormalities (e.g., toxic granulation/vacuoles).

Oil Immersion (100x) Examination

  • WBC Differential:

    • Conduct in a zig-zag pattern ensuring all WBCs are counted (don’t skip cells).

  • Evaluate RBCs for:

    • Normalcy, and types of abnormalities including:

      • Normocytic/normochromic

      • Anisocytosis (size variations)

      • Poikilocytosis (shape variations)

      • Hypochromasia (spherocytes)

      • Polychromasia (blue-stained immature cells)

  • Platelet estimate:

    • Count in 10 fields, multiply by 20.

  • Correction for nRBCs:

    • If more than 10 nRBCs per 100 WBCs, use corrected formula:

      • Corrected WBC count = WBC count (x10^9/L) x 100 / (nRBCs + 100)

Tables for Reference

Estimated White Blood Cell Count From Peripheral Smear

  • Counts:

    • 2-4 --> 4.0-7.0 x 10^9/L

    • 4-6 --> 7.0-10.0 x 10^9/L

    • 6-10 --> 10.0-13.0 x 10^9/L

    • 10-20 --> 13.0-18.0 x 10^9/L

Platelet Estimate From Peripheral Smear

  • Average Number of Platelets per 100x Field:

    • 0-1 --> Less than 20,000/L

    • 1-4 --> 20,000-80,000/L

    • 5-8 --> 100,000-160,000/L

    • 10-15 --> 200,000-300,000/L

    • 16-20 --> 320,000-400,000/L

    • Greater than 21 --> Greater than 420,000/L