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

Study Notes

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.

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.

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.

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.

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.