The CBC consists of measuring the following parameters:
- number of leukocytes;
- differential white blood count/leukocyte formula;
- number of erythrocytes;
- haemoglobin;
- haemoglobin concentration: mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC); these 2 may also be referred to as erythrocytes indices;
- haematocrit;
- erythrocytes indices: mean corpuscular volume (MCV), mean erythrocyte haemoglobin (MCH), and red cell distribution width (RDW);
- platelet count and platelet indices: average platelet volume (VTM) and platelet distribution width (PDW);
- number of reticulocytes.
WHITE BLOOD CELLS/LEUKOCYTES
White blood cells (WBC)/leukocytes/leucocytes are the cells of the immune system involved in protecting the body against foreign invaders and infectious diseases. There are 5 categories: basophils, eosinophils, lymphocytes, monocytes and neutrophils, each of them fulfilling a specific function. All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells.
White blood cell count: number of white blood cells in the blood. Differential white blood cell: the percentage of each type of white blood cells present in the blood.
Granulocytes: a type of white blood cells that have small granules, containing proteins. The specific types of granulocytes: neutrophils, basophils, eosinophils. Granulocytes, specifically neutrophils, help the body fight bacterial infections.
Mast cell: mastocyte/labrocyte; a resident cell of connective tissue that contains granules rich in histamine and heparin. Mast cell: a type of granulocyte derived from the myeloid stem cell; a part of the immune and neuroimmune systems.
BASOPHILS
Basophils and mast cells are important factors in allergic inflammation and other immune and inflammatory phenomena. These express on their surface an isoform of the receptor with high IgE affinity (when bound to the sensitising allergen or anti-IgE antibodies, both basophils and mast cell are activated, inducing mediators synthesis and secretion). Hence, basophils and mast cells are important factors in allergic inflammation and other immune and inflammatory phenomena.
Basophils are the largest granulocytes, much larger than the eosinophils or the neutrophils. Basophils are structurally similar to the mast cells, but generally speaking, basophils have fewer granules than the mast cells and have a more homogeneous morphology than the mast cells.
Basophils occur in most inflammatory reactions, especially those involving allergies. Heparin, contained in basophils, is an anticoagulant that prevents blood from clotting too quickly.
EOSINOPHILS
The nucleus is usually bilobed, but 3 or more lobes are often seen. They are in small number in healthy individuals, but become predominant in the blood and tissues in association with various allergic diseases (asthma), parasites or malignancies. Eosinophils contain at least 5 different types of intracytoplasmic granulations. Allergen/parasite-induced eosinophilia: dependent on the T-cells; mediated by cytokines released by the sensitized lymphocytes.
The "eosinophils" name comes from the fact that these cells have an affinity for acid dyes (eosin), which gives them a specific red-brick coloration. They contain small cytoplasmic granules, which contain many active substances, such as histamine, ribonuclease and eosinophil peroxidase.
NEUTROPHILS
- play a major role in the body's primary anti-infective defence by phagocytizing and digesting microorganisms. Their improper activation may lead to damage to the body's normal tissues by releasing enzymes and pyogenic agents.
Upon infection, chemotactic agents are produced, which cause migration of neutrophils to the site of infection. The defensive functions of neutrophils are activated, with phagocytosis of the agent, followed by the release of granules into the phagocytosis vesicle and destruction of the infectious agent.
Immature forms of neutrophils: bands cells; non-segmented polymorphonuclear neutrophils.
Mature forms of neutrophils: segmented neutrophils; polymorphonuclear neutrophils.
LYMPHOCYTES
Although some morphological characteristics (size, granularity, nucleolar-cytoplasmic ratio) differentiate lymphocyte populations from each other, they do not provide indications of their type and function.
Lymphocytes:
- 65-80%: T cells (maturing in the thymus, where they migrate from the medullary level);
- 8-15%: B cells (maturing in the bone marrow);
- 10%: natural killer cells (some of them are identical with the large granular lymphocytes).
Plasma cells are completely differentiated B cells and are not normally present in the blood. Intermediate cells (lymphoplasmocytes): common in viral infections or in immunological diseases with hypergammaglobulinemia.
B cells control the humoral immune response mediated by antibodies specific to the offensive antigen. Memory B cells: long lifespan; do not produce antibodies until antigenic restimulation, when they respond to much lower doses of antigen, proliferate clonally and produce 7-10 times more antibodies than unexposed B cells.
T cells: involved in the cell-mediated immune response; include CD4+ helper T cells, CD8+ suppressor T cells and cytotoxic T cells. T-cells circulate until they encounter specific antigens; a critical part in immunity against foreign substances.
NK cells are effector lymphocytes of the innate immune system that control several types of tumors and microbial infections.
MONOCYTES
- the largest cells in the blood; are part of the mononuclear/reticuloendothelial phagocytic system (composed of: monocytes, macrophages and their medullary precursors).
Monocytes and macrophages produce numerous bioactive factors: enzymes, complement factors, coagulation factors, reactive oxygen and nitrogen species, angiogenetic factors, binding proteins, bioactive lipids, chemotactic factors, cytokines and growth factors.
Monocytes: a type of phagocytic leukocytes (agranulocytes) that are part of the innate immune system of vertebrates (including humans). The precursors of monocytes: monoblasts, which originate in the bone marrow; they initially evolve into pro-monocytes, then into monocytes.
Monocytes: part of the monocyte-phagocytic system. Once migrated into tissues, monocytes can be differentiated into:
- macrophages (tissues - spleen, alveoli etc);
- histiocyte - connective tissues;
- microglia - CNS;
- osteoclasts - bones;
- Kupfer cells - liver;
- dendritic cells - Langerhans cells (skin), digestive tract, lungs etc.
Macrophages are a type of white blood cells that engulfs and digests anything that does not have, on its surface, proteins that are specific to healthy body cells (phagocytosis).
DIFFERENTIAL WHITE BLOOD CELL COUNT/LEUKOCYTE FORMULA
The leukocyte formula - a blood test that assesses the number of the 5 types of leukocytes, expressed as a percentage and in absolute numbers. The leukocyte formula is used in diagnosing the specific cause of some diseases.
Normal leukocyte values, in percentage:
- neutrophils: 60-70%
- basophils: 0-1%
- eosinophils: 1-4%
- monocytes: 4-8%
- lymphocytes: 25-30%
Leukocytes: also divided into 2 main groups, according to the presence/absence of granulations in the cytoplasm:
- granulocytes: neutrophils, eosinophils and basophils; also called polymorphonuclears (multilobed nucleus);
- non-granulocytes: lymphocytes and monocytes; no distinct cytoplasmic granules and have non-lobulate nucleus; also called mononuclear leukocytes.
RED BLOOD CELLS/ERYTHROCYTES
- the most numerous cells in the blood, anucleate upon maturity and necessary for tissue respiration. Main function: transporting oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. Erythrocytes increase and decrease along with the haemoglobin and the haematocrit. Shape: round with narrow centers resembling a donut without a hole in the middle.
- red blood cells formation: in the red bone marrow of bones. Stem cells in the red bone marrow: hemocytoblasts and give rise to all of the formed elements in the blood. If a cell commits to becoming a cell called a proerythroblast, it will develop into a new red blood cell.
HAEMOGLOBIN
- the protein molecule in red blood cells that carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues back to the lungs;
- 4 protein molecules (globulin chains) connected together, make up the haemoglobin molecule. Normal adult haemoglobin: 2 alpha-globulin chains and 2 beta-globulin chains. Foetuses and infants: 2 alpha chains and 2 gamma chains (gamma-chains gradually replaced by beta-chains upon growth);
- each globulin chain: iron-containing porphyrin compound termed heme. Embedded within the heme: an iron atom (vital for transporting oxygen and carbon dioxide; gives the red colour of the blood).
- haemoglobin also gives the shape of the red blood cells; abnormal haemoglobin structure can disrupt the shape of the red blood cells and implicitly their function.
HAEMOGLOBIN CONCENTRATION
- MEAN CORPUSCULAR HAEMOGLOBIN/MCH - average quantity of haemoglobin in a single red blood cell;
MCH (pg) = [ Haemoglobin (g/dL) / RBC (mil/uL) ] x 10
- MEAN CORPUSCULAR HAEMOGLOBIN CONCENTRATION/MCHC - concentration of haemoglobin in a certain amount of blood;
MCHC (g/dL) = [ Haemoglobin (g/dL) / HCT (%) ] x 100%
HAEMATOCRIT
- HCT: volume of red blood cells relative to the volume of blood, expressed as a percentage; example: HCT 25%: 25 ml of red blood cells in 100 ml of blood.
HCT value is used to determine erythrocyte indices: mean erythrocyte volume, mean corpuscular haemoglobin concentration, mean corpuscular haemoglobin. All of these together are useful for the differential diagnosis of various types of anaemia.
- also called Packed Cell Volume/PCT
ERYTHROCYTES INDICES
- MEAN CORPUSCULAR VOLUME (MCV)/MEAN CELL VOLUME/MEAN ERYTHROCYTE VOLUME: average size of red blood cells in a blood sample. MCV represents the volume occupied by a single erythrocyte. It is a useful index for classifying anaemias and depends on plasma osmolarity and the number of erythrocyte divisions.
MCV (fL) = [ Hct (%) / RBC (mil/uL) ] x 10
- MEAN ERYTHROCYTE HAEMOGLOBIN/HEM/MCH - see "Haemoglobin concentration";
- WIDTH OF ERYTHROCYTES DISTRIBUTION/RDW - a measurement of the range in the volume and size of the red blood cells (difference in size between the smallest and largest red blood cells in a sample); differentiates between different types of anaemia.
PLATELETS
Platelets form blood clots to slow down blood loss, to prevent infection and to promote healing. When an injury occurs, platelets aggregate to plug the wound and send hormone signals through the blood to attract protein clotting factors, which assists in repairing the injury.
Platelets are small, anucleate cells, produced in the bone marrow from the fragmentation of megakaryocytes (are actually pieces of them). Platelets have a role in haemostasis (participating in thrombi formation), as well as a source of growth factors.
- PLATELET COUNT measures the total number of platelets in the blood.
- MEAN PLATELET VOLUME (MPV) - measure of the average size of the platelets/thrombocytes. The MPV indicates the uniformity of platelet population size.
- PLATELET DISTRIBUTION WIDTH (PDW) - reflects how uniform the platelets are in size. PDW is a measurement of the variability in platelet size distribution in the blood. A normal PDW indicates platelets that are mostly the same size, while a high PDW means that platelet size varies greatly, a clue that there is platelet activation and has been associated with vascular diseases and certain cancers.
RETICULOCYTES
- newly produced, non-nucleated, relatively immature red blood cells, that contain residual nucleic acids (RNA); a reticulocyte count (number/percentage of reticulocytes in the blood) - a reflection of recent bone marrow function/activity.
Blood-forming (hematopoietic) stem cells differentiate and develop, eventually forming reticulocytes and finally becoming mature red blood cells. Reticulocytes are visually slightly larger than mature red blood cells. Unlike most other cells in the body, red blood cells have no nucleus, but reticulocytes still have some remnant genetic material (RNA). As reticulocytes mature, they lose the last residual RNA and most are fully developed within one day of being released from the bone marrow into the blood. The reticulocyte count shows the bone marrow's ability to produce red blood cells.
SUMMARY IMAGE OF BLOOD CELLS:
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