Complete blood count (CBC):- Part 2 – Red Blood Cells Morphology, Functions, Interpretations and Hemoglobin Formation

Complete blood count (CBC)
Sample for CBC
- Takes blood in the EDTA.
- Direct blood smears for the appreciation of the RBC morphology.
Indications
- To diagnose the various types of anemia.
- Any other abnormality of white blood cells and platelets.
Pathophysiology of the red blood cells:
Red blood cell metabolism is important for its survival and function.
- Red blood cell metabolism is dependant upon:
- Red blood cell membrane:
- The RBC membrane consists of proteins and phospholipids.
- It can change the shape without any fragmentation or damage.
- The RBC membrane consists of 50% proteins, 20% phospholipids, 20% cholesterol, and 10% carbohydrates.
- Carbohydrates are only in the outer layer.
- Red blood cell membrane:
- Hemoglobin formation, structure, and function.
- Normal hemoglobin formation is dependant upon:
- Adequate iron supply and delivery.
- Adequate formation of the precursor of the heme, protoporphyrins.
- Adequate synthesis of globin.
- Hemoglobin (Hb) is a conjugated globular protein with a molecular weight of around 64.4 Kd.
- This protein is 95% of the RBC’s dry weight or 33% of the RBC’s weight by volume.
- Around 65% of the Hb synthesis occurs during the nucleated stage of RBC maturation, and 35% occurs during the reticulocyte stage.
- Hemoglobin genes are present on chromosomes number 16 and 11.
- Normal Hemoglobin consists of 2 α- chains and 2- β chains with four protoporphyrin rings with Fe++ (ferrous).
- Hemoglobin is the main oxygen carrier to the cells and the tissue.
- This also takes CO2 back to the lung.
- This protein is 95% of the RBC’s dry weight or 33% of the RBC’s weight by volume.
- Normal hemoglobin formation is dependant upon:
- The energy pathways for RBCs metabolism.
- Active RBC metabolic pathways are important for the production of an adequate amount of ATP level, which is necessary for:
- Hemoglobin function.
- RBC membrane integrity and change in shape.
- An adequate amount of reduced pyridine nucleotides.
- Maintaining the RBC volume.
- RBC generates energy almost mainly from the anaerobic breakdown of glucose.
- Mature RBC has a limited ability to metabolize fats and amino acids.
- RBC ATP needs 90% is generated by the Embeden-Meyerhof glycolytic pathway.
- 5 to 10% of the energy is provided by the metabolism of glucose – hexose monophosphate shunt.
- Active RBC metabolic pathways are important for the production of an adequate amount of ATP level, which is necessary for:
- RBC life history:
- RBCs from the front side are round but, when seen from the side view, look biconcave.
- This can be given the example of doughnut-shaped with depression in the center.
- It measures 7 to 8 µm in diameter.
- RBCs mature in the bone marrow, and when it comes to the peripheral blood, it takes 3 to 5 days.
- The RBCs live in the peripheral blood for around 120 days. After completing their life, these are cleared in the spleen, liver, and bone marrow.
- Functions of the red blood cells:
- The RBCs’ main function is to carry oxygen from the lung (arterial blood) to the cells and the tissues. The oxygen is carried with a chemical combination with the hemoglobin.
- At the tissue level, oxygen is exchanged with the CO2 and brings CO2 in venous blood to the lungs.
- Normally O2 exchange occurs between 95% saturation in arterial blood with a mean arterial O2 tension of 95 mmHg and 70% saturation in venous blood with a mean venous O2 tension of 40 mmHg.
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- The RBCs have to be in close contact with the tissue and successful gaseous exchange to carry hemoglobin. RBCs must be able to pass through the microcirculation.
- RBC traveling in the microcirculation in 120 days which is roughly 300 miles (480 Km).
- To fulfill all these above functions, the RBCs are flexible and biconcave discs.
Peripheral blood smears give a lot of information about the RBCs morphology and effects of various drugs or different types of anemias.
- Anemia workup includes:
- Hb concentration.
- Hematocrit (Hct).
- RBC indices.
- Reticulocytes count.
- Evaluation of the peripheral blood smear.
- Bone marrow can also be advised to classify the anemia.
- Defects of the RBCs formation and reason for anemia (Etiology):
- Deficiency diseases.
- Refractory anemia due to ineffective erythropoiesis.
- Defect of the bone marrow due to hypoproliferative anemias.
- Excessive loss of the blood like:
- Hemolysis.
- Hemorrhage.
- Disorders of the RBCs leading to various types of anemias:
- Iron-deficiency anemia.
- Sideroblastic anemia.
- Anemia of chronic diseases.
- Thalassemia syndrome.
- Pernicious anemia.
- Folic acid deficiency anemia.
- Aplastic anemia.
- Pure red cell aplasia.
- Refractory anemia.
- Paroxysmal nocturnal hemoglobinuria.
- Hemolytic anemias.
- Hemorrhagic anemia.
- Hereditary spherocytosis.
- Hereditary elliptocytosis.
- Glucose-6-phosphate dehydrogenase deficiency.
- Pyruvate kinase deficiency.
- Sickle cell anemia and disease.
- Autoimmune hemolytic anemia.
Red blood cells assessment is based on:
- RBCs volume:
- Normal MCV RBCs are called normocytic.
- High MCV RBCs are called macrocytic.
- Low MCV RBCs are called microcytic.
- Hemoglobin contents:
- Normal Hb and MCHC are called normochromic.
- High MCHC RBCs are called hyperchromic.
- Low MCHC RBCs are called hypochromic.
Red blood cell indices are:
Clinical presentation | MCV fl |
MCH pg |
MCHC % |
Normal | 80 to 100 | 26 to 32 | 32 to 36 |
Normocytic anemia | 82 to 92 | 25 to 30 | 32 to 36 |
Microcytic anemia | 50 to 80 | 12 to 25 | 25 to 30 |
Macrocytic anemia | 95 to 150 | 30 to 50 | 32 to 36 |
Microscopic evaluation:
Microscopic examination of the peripheral blood smears give information about:
- The size (anisocytosis).
- The shape (poikilocytosis).
- The color (hypochromic or hyperchromic).
- Intracellular inclusions.
- Microscopic examination:
- First scan under the low power 10x and note:
- Staining quality of the smear.
- Also, check the center and edges of the slide to see there is no clumping of RBCs, WBCs, and platelets for the good distribution of the cells on the smear.
- Scan for the abnormal cells.
- Find the area where the RBCs should not touch each other.
- The RBCs should have a gradual central pallor.
- Scan the smear in high power 40x and note:
- WBCs abnormality.
- Can estimate WBCs count.
- Evaluate the RBCs morphology.
- Scan the smear in oil immersion 100x and note:
- Evaluate the RBCs anisocytosis, poikilocytosis, hypochromasia, polychromasia, and inclusion.
- Can evaluate the platelets count.
- WBCs differential can be done.
- First scan under the low power 10x and note:
The following table explains the RBCs morphology changes and interpretation: