Hematology Quiz: WBC Histogram Analysis

Complete Blood Count (CBC) Interpretation

• CBC is the most common test in clinical medicine.
• It's used to determine the type and severity of blood cell abnormalities.
• Modern CBCs are fully automated and highly reproducible.
• Correct CBC interpretation reduces unnecessary blood smears.
• It aids in provisional diagnosis of red blood cell (RBC) and white blood cell (WBC) diseases.

Components of Automated CBC

• Blood count parameters include hemoglobin (Hb), hematocrit (Hct), red blood cells (RBC), white blood cells (WBC), and platelets.
• Red cell indices: Mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), red cell distribution width (RDW).
• WBC differentials (granulocytes, lymphocytes, monocytes, eosinophils, basophils, and neutrophils).
• Platelets count and indices.
• Reticulocyte count.

Advantages of Automation

• Increased efficiency and streamlined workflow.
• Increased productivity.
• Increased test volumes without extra resources.
• Reduced turnaround time (TAT) and improved service.
• Lower costs.

Basic Principles of Automated Blood Cell Analyzers: Electrical Impedance

• Red blood cells are poor conductors of electricity.
• Diluents are good conductors.
• This difference forms the basis of cell counting systems.
• Coulter Principle: The conventional technique for cell counting.
• Blood flows through a narrow aperture between two electrodes.
• Change in impedance is proportional to cell volume, enabling cell counting and volume measurement.
• 10,000 cells per second can be counted in typical analysis.
• Process takes less than a minute.

Light Scattering

• Microscopic particles, like blood cells, scatter incident light into different angles.
• Correlating generated optical signals classifies cells in multidimensional spaces.
• Forward scatter (low angle) primarily depends on cell size.
• Sideward scatter (90 degrees) predominantly reflects nuclear segmentation and cytoplasmic granules.

Automated Differential Count

• Modern differential counters use flow cytometry in conjunction with full blood counting.
• Automation allows for three-part or five-to seven-part differential counts.
• Counts are performed on diluted whole blood, where red blood cells may be lysed or rendered transparent.
• Analysis often involves dye binding to granules or cellular enzyme activity (like peroxidase).

Three-Part Differential

• Categorizes cells as granulocytes ("large cells"), lymphocytes ("small cells"), and monocytes ("middle cells").
• In practice, some eosinophils and basophils may be counted in the monocyte category.
• Some three-part diffs categorize leukocytes by ratio (small, middle, large).

Five and Seven-Part Differentials

• Classifies blood cells further, including immature granulocytes, blasts, and atypical lymphocytes.
• Automated instruments can flag potential abnormalities with elevated numbers of certain cell types.
• Often counts neutrophils, eosinophils, basophils, lymphocytes, monocytes, and sometimes, additional cell types.

Automated Nucleated Red Blood Cell (NRBC) Count

• NRBCs affect white blood cell (WBC) accuracy in some counting machines.
• Historically, NRBC enumeration was done manually via blood smears.
• Automated methods stain NRBCS and distinguish them from WBCs; if nuclear size is too small, then it is not distinguishable.

Flagging of Automated Blood Counts

• A "flag" signals inconsistencies in machine analysis.
• Operators need manual verifications if flagged.
• Flags occur when analyzer detects possible abnormalities, and microscopic examination is needed.

Measurement of Hemoglobin

• Some machines measure hemoglobin (Hb) by modifying the cyanide method (HiCN).
• They dilute blood with reagents like potassium cyanide and ferricyanide.
• Hemoglobin (Hi and HbCO) are converted to HiCN, absorbance at 540 nm is measured.

Erythrocyte Sedimentation Rate (ESR)

• Measures how quickly red blood cells settle in plasma.
• Consists of 3 phases: aggregation, sedimentation, and packing.
• Factors affecting speed: plasma protein composition, erythrocyte size/shape, erythrocyte concentration.
• Elevated ESR is common in inflammatory diseases, while low ESR can be tied to conditions with few/small or abnormal red cells.

RBC indices

• RBC count: Measures the actual number of red blood cells, normal for adults male = 5 +/- 0.5, females = 4.3 +/- 0.5
• Low RBC count: Often indicative of anemia due to blood loss, impaired production, or increased destruction.

Hematocrit (HCT):

• The ratio of red blood cells to the total blood volume.
• Expressed as a percentage.
• High or low HCT correlates with high or low RBC counts.
• Normal range differs between males and females.

Higher than Normal Hematocrit

• Abnormal increase in red blood cells (erythrocytosis).
• Conditions like polycythemia vera.
• Low oxygen levels (hypoxia), may be observed at high altitudes or due to heart/lung diseases, body increases red blood cells to compensate for low oxygen.

Lower than Normal Hematocrit

• Insufficient supply of healthy red blood cells (anemia).
• Long-term illness, infection, leukemia, lymphoma, and other blood disorders.
• Acute kidney disease leading to reduced production of red blood cells.
• Pregnancy (additional fluid retention).

Hemoglobin (Hb)

• The protein in red blood cells that carries oxygen.
• Normal ranges vary by age and sex.
• Low levels indicate anemia, high levels indicate polycythemia.

Mean Corpuscular Volume (MCV)

• Average volume of red blood cells.
• Important for classifying anemia (microcytic, normocytic, or macrocytic).
• Based on hematocrit and red blood cell count.

Mean Cell Hemoglobin (MCH)

• Average mass of hemoglobin per red blood cell.
• Calculated using hemoglobin level and red blood cell count.
• Low levels commonly associated with iron-deficiency anemia.

Mean Corpuscular Hemoglobin Concentration (MCHC)

• Concentration of hemoglobin in a defined volume of red blood cells.
• Low levels (hypochromic) often reflect iron-deficiency anemia.
• High levels (hyperchromic) are uncommon but may occur in situations like autoimmune hemolytic anemia.

Red Cell Distribution Width (RDW)

• Measures variation in red blood cell size.
• Aids in differentiating anemia types (single cause vs. mixed causes).
• High RDW often seen in conditions like iron-deficiency anemia or conditions with mixed causes of anemia for example, anemia of chronic disease or thalassemia.

WBC/Differential Count

• Normal WBC counts differ by age (usually higher in children).
• Low WBC counts (leukopenia) can arise from various factors (infection, drug use, certain cancers).
• High WBC counts (leukocytosis) can result from infections, inflammation, certain cancers, or other causes.

Platelet (PLT) Count

• Normal platelet counts range differently in adults and children.
• Elevated counts (thrombocytosis) may result from reactive conditions, or be associated with blood cancers, inflammatory conditions, infections, and reactive processes.
• Low counts (thrombocytopenia) are tied to processes such as platelet consumption, failure of production, or peripheral destruction.

Platelet Indices

• Plateletcrit (PCT): Percentage of blood occupied by platelets.
• Mean platelet volume (MPV): Average volume of platelets.
• Platelet volume distribution width (PDW): Variability in platelet size.
• Platelet larger cell ratio (P-LCR/PLCR): Percentage of larger platelets in circulation.

Histogram

• Visual representation of blood cell distribution.
• Helps identify possible anomalies in cell size, shape, and counts that may lead to blood disorders.
• The histogram can show abnormal ranges for various cell types.

WBC Histogram

• Illustrates distribution of different white blood cell types, such as lymphocytes, monocytes, and neutrophils (and basophils and eosinophils).
• Normal graphs show different patterns based on expected cell distribution.

RBC and Platelet Distribution Curve

• Blood cells (RBCs and platelets) are counted together.
• A line separates platelet and red blood cell regions in a histogram.