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Hematology

Cell Counts

Overview of Cell Counts

  • Definition: A fundamental laboratory test used to enumerate the cellular components of blood and body fluids
  • Clinical Significance:
    • Diagnosis and monitoring of a wide range of medical conditions, including:
      • Infections
      • Inflammatory disorders
      • Hematologic malignancies
      • Bone marrow disorders
      • Bleeding disorders
  • Types of Cell Counts:
    • Complete Blood Count (CBC): Measures the number of RBCs, WBCs, and PLTs in whole blood
    • Body Fluid Cell Counts: Measures the number of RBCs and TNCs (total nucleated cells) in various body fluids (e.g., cerebrospinal fluid, synovial fluid, serous fluids)
    • Reticulocyte Count: Measures the number of immature red blood cells (reticulocytes) in whole blood
  • Methods:
    • Manual Cell Counts: Performed using a microscope and a specialized counting chamber
    • Automated Cell Counts: Performed using automated hematology analyzers

Manual Cell Counts

  • Principle:
    • A known volume of diluted fluid is placed in a specialized counting chamber (hemocytometer)
    • The cells are counted within a defined area of the counting chamber under a microscope
    • The cell count per unit volume is calculated using a formula that takes into account the dilution factor and the area of the counting chamber

Automated Cell Counts

  • Principle:
    • Automated hematology analyzers use various technologies to count and characterize blood cells
    • Common technologies include:
      • Electrical Impedance (Coulter Principle): Cells pass through a small aperture, disrupting an electrical current; the number and size of the disruptions are measured
      • Optical Scatter: Cells pass through a light beam, and the amount and angle of light scattered are measured; provides information about cell size, shape, and granularity
      • Flow Cytometry: Cells are stained with fluorescent dyes and passed through a laser beam; the fluorescence intensity and scatter patterns are measured

Reticulocyte Counts

  • Principle: Measurement of the number of immature red blood cells (reticulocytes) in the peripheral blood

Quality Control (QC) and Troubleshooting

  • Manual Cell Counts:
    • Use calibrated pipettes and equipment
    • Maintain clean equipment
    • Use proper staining techniques
    • Count an adequate number of cells
    • Follow established procedures
    • Perform duplicate counts to assess precision
  • Automated Cell Counts:
    • Perform daily instrument calibration and maintenance
    • Run control materials at regular intervals
    • Review control results and take corrective action if necessary
    • Investigate flags and alarms generated by the instrument
    • Correlate automated results with peripheral blood smear findings
  • General Troubleshooting:
    • Identify and correct pre-analytical errors (e.g., clotted sample, improper collection)
    • Repeat the test on a fresh sample
    • Perform manual cell counts to confirm automated results
    • Consult with a supervisor or pathologist if the cause of the discrepancy cannot be determined

Reporting Results

  • Report the cell counts in the appropriate units (e.g., cells/μL, x 10^9/L)
  • Include the reference range for each parameter
  • Note any abnormal results or flags
  • Document all quality control procedures and corrective actions taken

Key Terms

  • Cell Count: Enumeration of cells in a fluid sample
  • Hemocytometer: A specialized counting chamber used for manual cell counts
  • Dilution Factor: The ratio of the final volume to the initial sample volume
  • Reticulocyte: Immature red blood cell
  • Supravital Stain: A dye used to stain living cells
  • Electrical Impedance (Coulter Principle): A method for counting and sizing cells
  • Optical Scatter: A method for characterizing cells based on light scattering properties
  • Flow Cytometry: A technique for identifying and quantifying cells based on their surface markers and other characteristics