Red Blood Cell Formation and Characteristics

Erythropoiesis

• Erythropoiesis is the process of RBC formation, which takes place inside the bone marrow.
• The site of formation is the red marrow, and related terms include:
  • Erythron: the total mass of RBCs circulating in the peripheral blood and the bone marrow RBC precursors.
  • RBC mass: the erythrocytes in the circulation, total population present inside the circulation (blood vessel only).
  • Erythrokinesis: a term that describes the dynamics of RBC creation and destruction.

Reticulocytes

• Reticulocytes are immature RBCs that have a network of ribosomal RNA.
• Methods of counting reticulocytes include:
  • Supravital staining (e.g., methylene blue, brilliant cresyl blue)
  • Wright's staining

Erythrocytes

• RBC count is an important parameter in blood tests.
• RBC metabolic pathways include:
  • Anaerobic glycolysis ( Embden-Meyerhof pathway)
  • Hexose monophosphate shunt
  • Pentose phosphate pathway
• RBC anomalies include:
  • Anisocytosis (abnormal variation in RBC size)
  • Anisochromia (abnormal variation in RBC color)
  • Poikilocytosis (abnormal RBC shape)
  • RBC inclusion bodies (e.g., Howell-Jolly bodies, Cabot rings)

Hemoglobin

• Hemoglobinometry is the measurement of hemoglobin levels in the blood.
• Hemoglobin electrophoresis is a laboratory technique used to separate and identify hemoglobin types.
• Hemoglobin synthesis occurs in the bone marrow and is stimulated by erythropoietin.
• Hemoglobin derivatives include:
  • Carboxyhemoglobin (COHb)
  • Methemoglobin (MetHb)

Hematocrit and ESR

• Hematocrit is the proportion of RBCs in the blood.
• Hematocrit determination is done using a microhematocrit centrifuge.
• ESR (Erythrocyte Sedimentation Rate) is a measure of the rate at which RBCs settle at the bottom of a test tube.

Related Topics

• Rule of Three: a rough estimate of the RBC count, hemoglobin, and hematocrit.
• Erythrocyte Indices: a set of calculated values that describe the size and hemoglobin content of RBCs.
• Erythrocyte sedimentation rate (ESR): a measure of the rate at which RBCs settle at the bottom of a test tube.

Hemoglobinopathies

• Hemoglobinopathies are genetic disorders affecting hemoglobin structure or function.
• Examples include:
  • Sickle cell disease (HbS)
  • Thalassemia (α-thalassemia, β-thalassemia)

Thalassemia

• Thalassemia is a genetic disorder affecting hemoglobin production.
• Types of thalassemia include:
  • α-thalassemia (defective α-globin chain synthesis)
  • β-thalassemia (defective β-globin chain synthesis)

Hormones Related to Erythropoiesis

• Erythropoietin (EPO) is the chief stimulatory cytokine for RBCs.
• EPO is produced by the kidneys and stimulates the bone marrow to produce RBCs.
• Testosterone, growth hormone, and prolactin also stimulate erythropoiesis.
• Estrogen, on the other hand, inhibits erythropoiesis.

RBC Stages of Maturation

• BFU-E (Burst Forming Unit-Erythroid) is the earliest recognizable erythroid precursor.
• RBC maturation stages include:
  • Rubriblast (Pronormoblast)
  • Prorubricyte (Basophilic Normoblast)
  • Rubricyte (Polychromatic Normoblast)
  • Metarubricyte (Orthochromatic Normoblast)
  • Reticulocyte (mature RBC)

Nomenclature Systems

• There are three nomenclature systems used to describe RBC precursors:

  • Rubriblast, Normoblast, Erythroblast
  • Pronormoblast, Basophilic Normoblast, Polychromatic Normoblast, Orthochromatic Normoblast
  • Rubricyte, Metarubricyte, Reticulocyte### Reticulocyte

• An immature, non-nucleated RBC containing >2 blue-stained, granulofilamentous materials (reticulum) after supravital staining

• Continues to generate hemoglobin (last stage of hemoglobin synthesis)

• Normal maturation time in blood: 1 day

• Production of reticulocytes: 50 x 10^9/L/day

Reticulocyte Count

• Permits effective assessment of RBC production by the bone marrow
• Reference ranges:
  • Adults: 0.5-1.5%
  • Newborns: 1.8-5.8% (by 1-2 weeks of age, reference values are the same as for adults)

Reticulocytosis

• Increased reticulocyte count, considered as the first sign of accelerated erythropoiesis
• Observed in hemolytic anemias, iron deficiency anemia, thalassemia, and in acute and chronic blood loss

Mature Erythrocyte

• Shape: biconcave disk
• Thickness: 1.5-2.5 um
• Normal ratio of RBCs to WBCs: approximately 600:1
• Normal ratio of RBCs to Platelets: approximately 15:1

Methods of Counting Reticulocytes

• Routine Light Microscope Method
• Calibrated Miller Disk Method
• Flow Cytometry

Reticulocyte Count Calculation

• Total Reticulocytes observed / Total RBCs counted x 100

Corrected Reticulocyte Count (CRC)

• Corrects for the degree of anemia
• Formula: CRC = Reticulocyte count (%) x 0.45 L/L (Hct)

Absolute Reticulocyte Count (ARC)

• Actual number of reticulocytes in 1 liter of whole blood
• Formula: ARC = Reticulocyte count (%) x RBC count (x10^9/L)

Reticulocyte Production Index (RPI)

• Provides a further refinement of the CRC
• Calculation: RPI = CRC x Maturation time (in days)

Anemias

• Hemolytic anemia: ARC and IRF increase
• Chronic renal disease: ARC and IRF decrease
• Nutritional anemia: ARC and IRF may increase or decrease

Red Blood Cell Inclusions

• Howell-Jolly bodies: nuclear fragments

• Heinz bodies: denatured and precipitated hemoglobin

• Pappenheimer bodies: hemosiderin in the mitochondria

• Hemoglobin H: greenish-blue bodies### Abnormal Red Blood Cells

• Spherocytes: almost spherical in shape, lack central pallor, hereditary spherocytosis, autoimmune hemolytic anemia, burns, ABO HDN, and transfusion of stored blood

• Ovalocytes: oval-shaped RBCs, hereditary ovalocytosis, Southeast Asian ovalocytosis

• Elliptocytes: elliptical (cigar-shaped) RBCs, hereditary elliptocytosis, thalassemia, Mediterranean anemia

Stomatocytes

• Hereditary stomatocytosis
• Dehydrated hereditary stomatocytosis
• Xerocytes: dehydrated form of stomatocytes, appear to have puddled at one hand (half-dark, half-light), abetalipoproteinemia, McLeod syndrome
• Dacryocytes: pear-shaped or teardrop-shaped RBCs, primary myelofibrosis (PMF), myeloid metaplasia, chronic idiopathic myelofibrosis

Acanthocytes

• Irregularly spiculated surface, "Bassen-Kornzweig syndrome" and hereditary acanthocytosis
• Characterized by defective apo B synthesis, VLDL, LDL, chylomicron not found in plasma, McLeod syndrome, pyruvate kinase deficiency

Drepanocytes

• Sickle- or crescent-shaped RBCs, sickle cell anemia, hemoglobin SC disease, etc.
• Two forms of drepanocytes: 1) ISC (irreversible sickle cells) with crescent-shaped projections, 2) OAT-shaped cells with less pronounced projections

Schistocytes

• Fragmented RBCs, patients with artificial heart valves, uremia, severe burns, microangiopathic hemolytic anemias (MAHAs)
• Characterized by RBC fragmentation and thrombocytopenia, major MAHAs include TTP, HELLP, HUS, and DIC

Leptocytes

• RBCs with a centrally stained area with a thin outer rim of hemoglobin, liver disease, certain hemoglobinopathies, thalassemia, Mediterranean anemia

Other Abnormalities

• Bite cells: demonstrate a semicircular defect in their edge, resembles a bite mark, glucose-6-phosphate dehydrogenase (G-6-PD) deficiency
• Biscuit cells: folded RBCs, hemoglobin SC disease
• Semilunar bodies: as large as leukocytes, pale-pink staining ghost of the red cell, malaria and other conditions causing overt hemolysis
• Bronze elliptocytes: bipolar/central distribution of Hgb, sickle cell anemia
• RBC inclusion bodies: basophilic stippling, aggregated RNA, Wright stain (deep blue to purple), lead poisoning, arsenic poisoning, pyrimidine-5'-nucleotidase deficiency, anemias with ineffective erythropoiesis