Hematocrit and RBC Indices Quiz

Hematocrit and Packed Cell Volume (PCV)

• Hematocrit (PCV) measures the percentage of erythrocytes in total blood volume (vol/vol %).
• Determination involves centrifuging a blood-filled capillary tube, separating components based on density.

Principle of Hematocrit Determination

• Heavier RBCs settle at the bottom during centrifugation, forming the primary layer.
• WBCs and platelets form a lighter layer called the Buffy Coat above the RBCs.
• The plasma sits at the top of the separated layers.

Materials Required

• Venous blood anticoagulated with EDTA or capillary blood in heparinized tubes.
• Capillary tubes must be filled ¾ full and centrifuged within 6 hours.
• Essential items include a hematocrit centrifuge, clay sealant, and a microhematocrit reader.

Procedure Overview

• Mix anticoagulated blood and fill two microhematocrit tubes manually while avoiding air bubbles.
• Seal the tubes with clay and ensure a flat bottom.
• Place tubes in the centrifuge, balancing them and recording their positions.
• Centrifuge for 5 minutes at 11000 rpm to separate the blood components.
• Read the hematocrit, excluding the Buffy Coat; if it exceeds 2%, note it as packed WBC/plt volume.

Clinical Significance of PCV

• PCV is a quick test for detecting anemia and polycythemia.
• It helps estimate changes in hemodilution or hemoconcentration and is vital for MCV and MCHC calculations.
• Normal values: Newborns (53-65%), adult males (42-52%), adult females (37-47%).

Sources of Error in Hematocrit Measurement

• Mechanical Errors:

  • Incomplete sealing can lead to falsely low results.
  • Excessive pressure when stopping the centrifuge can falsely elevate RBC counts.
  • Insufficient centrifugation time can trap plasma, affecting readings.
  • Delayed removal of capillary tubes can cause RBC settlement and inaccurate results.

• Biological Errors:

  • Inclusion of the Buffy Coat leads to falsely elevated results.
  • Hemolysis can produce falsely decreased hemoglobin readings.
  • Spun microhematocrit is generally 1.3-3% higher than electronic results due to trapped plasma, notably in specific anemias.

RBC Indices

• Three key indices: MCV (Mean Corpuscular Volume), MCH (Mean Corpuscular Hemoglobin), MCHC (Mean Corpuscular Hemoglobin Concentration).
• They provide insights into erythrocyte conditions and assist in diagnosing different types of anemia.

Mean Corpuscular Volume (MCV)

• Indicates volume of erythrocytes: Normal range is 80-100 fl (femtoliter).
• Calculated as MCV = (PCV / RBC count) x 10.
• MCV classifications:
  • Normocyte (80-100 fl): Normal variations, normocytic anemias.
  • Microcyte (<80 fl): Indicates microcytic anemias like iron deficiency.
  • Macrocyte (>100 fl): Associated with macrocytic anemias like Vitamin B12 deficiency.

Mean Corpuscular Hemoglobin (MCH)

• Measures hemoglobin content per erythrocyte: Normal range is 27-32 pg (picogram).
• MCH calculated as MCH = (Hb / RBC count) x 10.
• MCH classifications:
  • Normochromic (27-32 pg): Normal and normochromic anemias.
  • Hypochromic (<27 pg): Present in hypochromic anemias like iron deficiency.
  • Hyperchromic (>32 pg): Linked to hyperchromic anemias like Vitamin B12 deficiency.

Mean Corpuscular Hemoglobin Concentration (MCHC)

• Determines hemoglobin volume fraction in erythrocytes: Normal range is 30-38%.
• MCHC formula: MCHC = (Hb / PCV) x 100.
• MCHC interpretations:
  • Normochromic (30-38%): Normal and normochromic anemias.
  • Hypochromic (<30%): Indicates hypochromic anemias like iron deficiency.
  • MCHC >38% usually indicates lab error, impossible biological concentrations.

Test your knowledge on hematocrit values, including how to manually determine them and the influencing factors. This quiz covers key concepts of packed cell volume in whole blood and its clinical significance. Make sure to brush up on the principles and applications before starting!