Hemoglobin, PCV, and Erythrocyte Indices

Complete Blood Count (CBC)

• Provides reliable, cost-effective values from automated or manual tests.

• Includes: Total RBC count, Packed Cell Volume (PCV)/Hematocrit, Plasma Protein Concentration (TP), Total WBC count, Hemoglobin (Hb) concentration, Erythrocyte Indices, Blood film evaluation.

• Hemogram = all CBC tests.

• Leukogram = Total WBC count & differential count.

Packed Cell Volume (PCV)

• Definition: Percentage of whole blood volume composed of erythrocytes.

• Purpose: Evaluates hydration, diagnoses anemia or erythrocytosis.

• Accuracy: Inherent error of $\pm1\%$.

• Equivalency: Hematocrit (Hct) expressed as volume (e.g., $PCV=42\%, Hct=0.42 L/L$).

• Procedure Essentials: Require microhematocrit tubes (red ring for heparin, blue ring no anticoagulant), sealant, centrifuge, reader card. Requires two tubes for quality control and balance.

• Sources of Error: Improper mixing, hemolysis, insufficient centrifugation.

• Reading PCV: Evaluate three layers:

  • Plasma Layer: Normal is clear; yellow (liver disease, hemolysis, dehydration, normal in ruminants), pink (hemolysis), white (lipemia).

  • Buffy Coat: Contains WBCs & platelets; normally white, $\approx1\text{ mm}$ thick; red if nucleated RBCs present.

  • PCV: Measured at the interface of RBC mass and buffy coat on a reader card, expressed as $\%$ and converted to $0.XX L/L$.

• Significance: Low PCV (anemia, diluted sample), High PCV (polycythemia, dehydration).

Plasma Protein Concentration

• Method: Uses refractometer on plasma from spun microhematocrit tubes.

• Procedure: Break tube above buffy coat, place plasma on refractometer, read TP scale in $g/100mL$ or $g/dL$ (convert to $g/L$).

• Normal Range: $50-80\text{ g/L}$ for most species.

• Interference: Lipemia and hemolysis falsely elevate results.

• Conversion: To convert $g/100mL$ or $g/dL$ to $g/L$, multiply by $10$.

Hemoglobin (Hb/Hgb) Concentration

• Function: Functional unit of RBCs, transports oxygen and carbon dioxide.

• Composition: Heme (iron) and globin (amino acid chains).

• Measurement Methods:

  • Automated analyzers.

  • Calculated from PCV: $Hgb (g/100mL) = PCV (\%) \div 3$. Convert to $g/L$ (multiply by $10$).

• Guidelines: Evaluate reticulocyte stain if Hgb is <120\text{ g/L} (dogs) or <80\text{ g/L} (cats).

Erythrocyte Indices (Mean Corpuscular Values)

• Purpose: Classify types of anemia.

• Includes: Mean Corpuscular Volume (MCV), Mean Corpuscular Hemoglobin (MCH), Mean Corpuscular Hemoglobin Concentration (MCHC).

• Required for Manual Calculation: PCV, Hgb, Total red blood cell count.

• Mean Corpuscular Volume (MCV):

  • Definition: Average size of individual RBCs.

  • Unit: Femtoliters (fL), where $1\text{ fL} = 10^{-15}\text{ L}$.

  • Calculation: $(PCV \div RBC\text{ count}) \times 10 = MCV (\text{fL})$.

  • Report as a whole number.

• Mean Corpuscular Hemoglobin (MCH):

  • Definition: Mean weight of Hgb in the average RBC.

  • Unit: Picograms (pg).

  • Calculation: $Hgb \div RBC\text{ count} = MCH (\text{pg})$.

  • Report with one decimal place. Not considered highly useful.

• Mean Corpuscular Hemoglobin Concentration (MCHC):

  • Definition: Concentration of Hgb in the average RBC.

  • Unit: $g/L$.

  • Calculation: $(Hgb\text{ (g/L)} \div PCV\text{ (\%)}) \times 100 = MCHC (\text{g/L})$.

  • Normal Range: $300-360\text{ g/L}$ for most mammals; $400-450\text{ g/L}$ for Camelidae and some sheep.

  • Report as a whole number.