Lab 2 (1)

Determination of Packed Cell Volume (PCV)

Introduction

  • Blood consists of liquid plasma and solid cellular components:

    • Red Blood Cells (RBCs)

    • White Blood Cells (WBCs)

    • Platelets

  • PCV (Hct) is the volume of RBCs in relation to whole blood (expressed as a percentage).

  • Example: 45% PCV means 45 mL of RBCs in 100 mL blood.

Measurement Significance

  • PCV reflects the number/size of RBCs and indicates overall blood health.

  • Accurate measure for detecting anemia (low PCV) or polycythemia (high PCV).

Factors Affecting PCV

  • Increase PCV: More or larger RBCs (e.g., osmotic pressure effects).

  • Decrease PCV: Fewer or smaller RBCs (e.g., microcytosis due to iron deficiency).

Normal PCV Values

  • Varies by age and sex:

    • Males: 40%–54%

    • Females: 37%–47%

    • Newborns: 53-65%

  • Critical value: 60%.

Purpose of PCV Experiment

  1. Understand PCV, determination methods, and clinical importance.

  2. Measure RBC volume in 100 mL blood.

  3. Assess oxygen transport capability of blood.

Principle of PCV

  • "Hematocrit" means to separate blood into cells and plasma using centrifugation.

  • Heavier cells settle, forming layers: plasma on top, RBCs at the bottom.

Methods to Measure PCV

  1. Microhematocrit Method:

    • Less blood and quicker results.

  2. Macrohematocrit Method:

    • More time-consuming and plasma trapping issues.

  3. Automated Method:

    • Uses automated hematology analyzers.

Materials Required

  • Microhematocrit tube, centrifuge, plastic seals, reader, lancet, 70% alcohol, cotton.

Procedure Overview

  • Clean fingertip with alcohol, fill tube using capillary action, seal, and centrifuge.

  • Post-centrifugation, observe three layers: plasma, buffy coat (WBCs and platelets), packed RBCs.

Reading PCV Value

  • Align tube parallel to the scale and read the RBC level excluding buffy coat.

Sources of Errors

  • Improper sealing of tubes.

  • Incorrect centrifuge settings.

  • Including buffy coat in readings leads to false elevations.

Factors Affecting Hct (PCV)

  1. Abnormal RBC morphology.

  2. Increased WBC counts.

  3. Higher Hct in people from high altitudes.

  4. Drugs like chloramphenicol reduce Hct.

  5. Pregnancy lowers values due to hemodilution.

  6. Dehydration affects Hct reliability.

Clinical Implications of High and Low PCV

  • Increased PCV:

    • Physiological: High altitude, physical exertion.

    • Pathological: Polycythemia vera, dehydration, congenital heart failure.

  • Decreased PCV:

    • Anemia, hemoglobinopathies, cirrhosis, hemorrhage, and malignancies.

Advantages and Disadvantages of Microhematocrit Method

  • Advantages:

    • Small sample volume, fast analysis, detects hemolysis.

  • Disadvantages:

    • Careful preparation needed, leakage can falsely lower results, clots may cause inaccuracies.