Hematocrit Value (Hct) and Packed Cell Volume (PCV)

Packed Cell Volume (PCV)

• Definition: The percentage of blood volume made up of red blood cells.
• Methods for detection:
  • Macro hematocrit method: uses Wintrobe hematocrit tube.
  • Micro hematocrit method: uses heparinized microhaematocrit capillary tube.
• Clinical significance:
  • Normal values:
    • Male: 42-52%.
    • Female: 37-47%.
  • Dehydration: Increase PCV.
  • Polycythemia: Increase PCV.
  • Overhydration: Decrease PCV.
  • Anemia: Decrease PCV.

Complete Blood Picture (CBC)

• Definition: The calculation of the cellular elements of blood.
• Uses automated hematology analyzer.
• Clinical significance:
  • Used to determine general health status.
  • Screens for, diagnoses, or monitors diseases and conditions affecting blood cells, such as anemia, infection, and bleeding disorders.

Red Blood Indices

• Mean cell volume (MCV): The average volume of red blood cell measured in femtoliters (fl).
  • Formula: MCV = PCV x 10 / RBC count.
• Mean cell hemoglobin (MCH): The average amount of Hb in a single red blood cell measured in picogram (pg).
  • Formula: MCH = Hb x 10 / RBC count.
• Mean cell Hb concentration (MCHC): The concentration of Hb per 100 ml of RBC measured in g/dl.
  • Formula: MCHC = Hb x 100 / PCV.

Osmotic Fragility Test

• Definition: Measures erythrocyte resistance to hemolysis while exposed to varying levels of dilution of a saline solution.
• Procedure:
  • Uses a series of test tubes containing decreasing concentrations of NaCl.
  • Adds 0.1 ml blood to each tube and observes the fluid color and RBCs precipitate.
• Clinical significance:
  • Increased fragility: Enzymatic deficiency (G-6-P-D deficiency), Hereditary spherocytosis.
  • Decreased fragility: Iron deficiency anemia, Thalassemia, Sickle cell anemia.

Erythrocyte Sedimentation Rate (ESR)

• Definition: The rate by which red cells sediment when blood is placed vertically in a narrow tube.
• Westergren Apparatus:
  • Uses Westergren Tube.
  • Leaves pipette for one hour and reads the height of the column of clear plasma above the precipitated RBCs.
• Normal values:
  • Male: 4-6 mm/h up to 15 mm/h.
  • Female: 8-10 mm/h up to 20 mm/h.
• Clinical significance:
  • Increases physiological in female during pregnancy, menstruation, and lactation.
  • Increases in pathological conditions such as tonsillitis, fractures, myocardial infarction, and rheumatoid arthritis.
  • Not a diagnostic test, but confirms presence or absence of inflammatory activity and monitors treatment progression.