Questions and Answers
What is the rule of three in the context of blood cell indices?
Hb x 3 = Hct
In relative polycythemia, why do RBCs appear increased?
Decreased plasma volume
What does absolute count refer to in a blood cell differential count?
Actual number of each cell type without respect to other blood components
What is the primary function of neutrophils in the bloodstream?
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What type of cell is responsible for antibody production?
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What does relative lymphocytosis indicate?
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In absolute polycythemia, what does the 'absolute' refer to?
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What is the function of eosinophils in the bloodstream?
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'Relative count' in a blood cell differential refers to what?
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'Absolute count' in a differential blood cell count refers to what?
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Study Notes
Differential Count
- A shift to the left in the differential count indicates the presence of immature granulocytes and may be found in disorders such as leukemias and bacterial infections.
- A shift to the right refers to an increased number of hypersegmented neutrophils.
Types of Differential Count
- Three-part differential: Granulocytes, Lymphocytes, and Monocytes.
- Five-part differential: Neutrophils, Lymphocytes, Monocytes, Eosinophils, and Basophils.
- The three-part differential is routinely used, but the five-part differential is performed if the WBC count is 10%, Basophil count is >2%, Monocyte count is >11%, or Lymphocyte count is > Neutrophil count, except in children.
Blood Cell Indices
- MCV (Mean Cell Volume): 80-100 fL, measures the average size of red blood cells.
- ↓ MCV (Microcytic): < 6 µm, associated with anemia of Chronic Inflammation, Thalassemia, Iron deficiency anemia, and Sideroblastic anemia.
- ↑ MCV (Macrocytic): > 8 µm, associated with Megaloblastic anemia and Vitamin deficiency.
Hematologic Procedures
- CBC (Complete Blood Count): includes RBC count, WBC count, Platelet count, Hemoglobin, Hematocrit, and Differential count.
- Blood Cell Indices: MCV, MCH, and MCHC.
Blood Cell Enumeration
- Manual methods: RBC count, WBC count, and Platelet count.
- Formula: CELL RBC count / WBC count / Platelet count = DILUTION 100 / 20 / 100 * TOTAL AREA COUNTED.
RBC Count
- Normal values: 5.0-6.5 x 10^12/L for newborns, 3.6-5.6 x 10^12/L for females, and 4.2-6.0 x 10^12/L for males.
- Increased in polycythemia vera and patients who live in places at a high altitude.
- Principle: Whole blood is diluted with isotonic diluting fluid to facilitate counting and prevent the lysis of RBCs.
Hemocytometer
- Consists of two identically ruled platforms.
- The space between the top of the platform and the cover glass is 0.1 mm.
- Each of the two platforms is composed of nine large squares, measuring 1 mm wide and 1 mm long.
Macrohematocrit Method
- Time-consuming, requires a large amount of blood, and contains a higher amount of trapped plasma.
Rule of Three
- Applies to specimens that have normocytic, normochromic erythrocytes.
- RBC x 3 = Hb, Hb x 3 = Hct +/- 3.
- 1 Hct = 0.34g Hb per 100 ml of WB, and 1 Hct = 107,000 RBCs/cu.mm.
Differential Counting
- Relative count: the amount of a cell type in relation to other blood components.
- Absolute count: the actual number of each cell type without respect to other blood components.
- Relative lymphocytosis: an increase in the percentage of lymphocytes, frequently associated with neutropenia.
- Absolute lymphocytosis: a true increase in the number of lymphocytes.
- Relative polycythemia: RBCs appear increased due to a decreased plasma volume.
- Absolute polycythemia: a true increase in red cell mass.
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