Reticulocytes: Immature Red Blood Cells

• Diagnosis of diseases is based upon laboratory analysis of bodily fluid

Reticulocytes

• Reticulocytes are immature red blood cells produced by the bone marrow.
• Reticulocytes are released into the bloodstream.
• Compared to fully mature RBCs, reticulocytes are larger and more spherical.
• Reticulocytes in the bloodstream circulate for about 2 days before maturing.
• Normally, about 1% to 2% of the red blood cells in the blood stream are reticulocytes.
• A reticulocyte count provides information about the rate at which the bone marrow is producing red cells.
• A normal count means that the production of reticulocytes is adequate.
• A decreased count means that the production of reticulocytes is not adequate.
• Determining if a lack of red cells in an anemic person is from a bone marrow problem, excessive bleeding, or red cell destruction is achieved with reticulocyte count information.
• Reticulocytes are counted manually with a microscope.
• The reticulocyte count may be expressed as a percentage of total RBCs or as an absolute number of reticulocytes in a given volume of blood.
• The reticulocyte count is normally between 0.5-2.5% for both adults and children.
• Reticulocyte counts for infants are normally between 2-5%.
• A low reticulocyte count indicates that the bone marrow is not producing a normal number of red blood cells.
• Low production could be from a lack of vitamin B12, folic acid, or iron in the diet as well as an illness affecting the bone marrow like cancer.
• Further testing is needed to diagnose the specific cause of the reticulocyte issue.
• The reticulocyte count elevates when the bone marrow produces more red cells in response to blood loss (bleeding) or destruction (hemolysis) as the underline cause of anemia.

Red Blood Cells (RBC)

• Normal RBCs are round, biconcave, contain no inclusions and have no nucleus.
• Normal RBC's also have a small area of central pallor, and show only a slight variation in size
• A normal red cell is 6-8 µm in diameter.
• Mature RBCs consist primarily of hemoglobin, about 90%.
• Erythrocytes are biconcave and anucleate in structure.
• Components of the red blood cells are Hemoglobin, Lipids, ATP, carbonic anhydrase.
• RBC membrane is composed of lipids and proteins.
• Additionally, there are numerous enzymes necessary for cell transport and oxygen viability within RBC's.
• The red cell is composed of water (55-65%), hemoglobin (30-36 %), and organic and inorganic materials less than 5%.
• The red cell membrane is composed of a triple-layered structure consisting of a lipid layer located between two protein layers (lipoprotein membrane).
• Erythrocytes primary function to serve as a carrier of Hb and Hb functions as a carrier of oxygen.
• Red Blood Cells (RBC) deliver oxygen to tissues in the body.
• RBC’s live for approximately 120 days.
• They are also called Erythrocytes.
• Normal red blood cell values at various ages are: 4.8 - 7.2 ×1012/L for newborns, 4.6 - 6.0 ×1012/L for adult males, 4.2-5.0 ×1012/L for adult females, slightly lower than normal adult values during pregnancy, and 3.8 – 5.5×1012/L for children.
• Enzymes are compounds helping the body break down food and build up substances.
• The red cell is active and capable of breaking down GLUCOSE to form energy, also needs energy to perform its functions
• Two key enzymes within RBC’s for creating energy are Glucose-6 Phosphate Dehydrogenase (G6PD) and Pyruvate kinase (PK).
• The relative amount of hemoglobin in the red cell is proportional to the amount of area in the central pallor.

Hemoglobin

• Erythrocytes contain a chemical substance known as hemoglobin.
• Hemoglobin is a pigment giving blood its red color, and contains iron(heme).
• Hemoglobin is a conjugated protein with heme and globin.
• Each molecule consists of 4 heme units and 4 globin units (a1,a2, β1 and β2) .
• Heme is the iron (Fe++) portion in the ferrous state and globin is the protein portion.
• Hemoglobin transports oxygen and helps exchange carbon dioxide.
• HEME is composed of protoporphyrin plus ferrous iron (Fe++).
• The basic structure of heme consists of 4 payroll rings linked together by 4 methane bridges.
• The properties of Hb depend upon maintaining iron in the reduced state (Fe++ ).
• GLOBIN is required for the formation of hemoglobin.
• Globing is synthesized in the cytoplasm of the precursors erythrocytes in the bone marrow
• Hemoglobin unites with oxygen.
• Hemoglobin’s mechanism transports oxygen via blood.
• Oxygen is transported to the body from the lungs.
• Carbon dioxide for disposal is picked up and returned.
• Iron in hemoglobin (hem) unites with oxygen to form oxyhemoglobin.
• Blood’s color is given by the process of carrying oxygen and carbon dioxide by hemoglobin .
• Arterial blood, high in oxygen, is bright red.
• Venous blood, high in carbon dioxide, is dark "purplish” red.
• Normal hemoglobin includes 3 types.
• Hemoglobin A (HbA) is the major normal adult hemoglobin molecule.
• HbA constitutes 97-98% of hemoglobin in blood and consists of 2 alpha (α2) and 2 beta (ß2) chains.
• Hemoglobin A2 (HbA2) is a minor adult Hemoglobin molecule.
• HbA2 is 2 to 3% of blood and has 2 alpha (α2) and 2 delta (δ2) chains.
• Hemoglobin F (HbF) is normal fetal.
• HbF is found in small quantities for the first years of life (up to 4%), as it’s normally 70-90% in newborns and reduces to <1% in adults.
• HbF consists of 2 alpha (a2) and 2 kama (y2) chains.
• Abnormal hemoglobin structure results from defects in amino acid chains. Examples are S, C, D, E, G, H, L, and Q.
• Normal hemoglobin values are 13.5 to 17.5 g/dl for males, and 11.5 to 15.5 g/dl for females.
• Normal Hemoglobin is between 14-18 g/dL for males, and 12-16 g/dL for females.
• Hb content is indicated by mean corpuscular hemoglobin (MCH).
• MCH is Hb (g/dl x 10) divided by RBC (millions/mm3).
• MCH is decreased in microcytic cells and increased in macrocytic cells.

Destruction of Old Red Blood Cells

• Normal life span of a red blood cell is approximately 120 days.
• Old Red blood Cells destroyed daily are replaced by new red cells, which are produced daily by the bone marrow.
• Site of Production is bone marrow.
• Approximately 1% of body's red blood cells are produced/destroyed daily so the total RBC mass remains constant.
• Sites of Destruction of RBC are Spleen, Liver, and by macrophages in Bone Marrow.

Extravascular Hemolysis

• Extravascularly, Hb is broken by the reticuloendothelial system (RES) down into heme and globin.
• Heme is broken down in RES to biliverden, then converted to bilirubin.
• Bilirubin is then secreted from RES, carried with the plasma protein (albumin), becoming (indirect-reacting bilirubin, unconjugated bilirubin, prehepatic bilirubin or insoluble bilirubin ).
• Unconjugated bilirubin is transported to the liver to conjugate with glucuronic acid and become cholebilirubin or called indirect bilirubin, conjugated bilirubin, hepatic bilirubin or soluble bilirubin.
• The order of Extravascular Hemolysis is: Hb becomes Heme and Globin, then Heme becomes biliverdin, then becomes Biliruben (unconjugated), and then unconjugated bilirubin becomes liver which becomes conjugated bilirubin.

Hematocrit

• The hematocrit (Hct) or (PCV) is the amount of packed cells in a sample of whole blood expressed in percent.
• Hematocrit can be used as a simple screening test for anemia.
• Hematocrit enables calculation of absolute values, when hemoglobin concentration and red cell count are known.
• Normal male hematocrit values are 40-50%.
• Normal female hematocrit values are 35-45%.
• Normal infant hematocrit values are 45-65%.