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© Dirk Biddle
The complete blood count (CBC) is a very common blood test. It evaluates the three major types of cells in blood: red blood cells (RBCs), white blood cells (WBCs), and platelets. The CBC typically has several parameters that are created from an automated cell counter. The most relevant include:
a) Red Blood Cells
Three tests; Red blood cell (RBC) count, the haemoglobin (Hgb) and haematocrit (Hct) test, and the mean (red) cell volume (MCV) measure, provides information about the number and quality of oxygen carrying red blood cells.
i) RBC, Haemoglobin (Hgb) and Haematocrit (Hct) - The haemoglobin count measures the amount of oxygen carrying protein contained within the red blood cells. The haematocrit test calculates the percentage of the blood volume occupied by red blood cells (Red blood cells comprise, on average, 45 percent of the blood's total volume). In most laboratories Hgb is actually measured, while the Hct is computed using the RBC measurement and the Mean Corpuscular Volume (MCV) measurement. Thus purists prefer to use the Hgb measurement as more reliable.
Low Hgb or Hct counts suggest anaemia. Anaemia can be due to nutritional deficiencies (particularly in those that do not eat red meat), blood loss, destruction of blood cells internally or failure to produce blood progenitors in the bone marrow. Low Hct and Hgb counts may also be signs that your medication is causing a loss of blood from your stomach and passing through your bowel. If you have chronic inflammation (such as in a vasculitis condition), the number of red blood cells usually is low. Alternatively, high Hgb can occur due to lung disease, living at high altitude, or excessive bone marrow production of blood cells. Hematocrit levels may be high with dehydration.
ii) Mean Corpuscular Volume (MCV) helps diagnose a cause of anaemia. Low values suggest iron deficiency, high values suggest either deficiencies of B12 or folate, ineffective production in the bone marrow, or recent blood loss with replacement by newer (and larger) cells from the bone marrow.
b) White Blood Cells
White Blood Cell (Differential) Count (WBC) - measures the relative numbers of white blood cells (WBCs) in the blood. WBCs (leukocytes) help the body fight infection (when you have an infection, your body makes more white blood cells). High or abnormal white blood cell counts may indicate a bacterial, viral, or fungal infection (and these can cause the WBC count to increase or decrease dramatically) or that there is an inflammation or other stress in the body. The WBC count is also increased in certain types of leukaemia. Low WBC counts can be a sign of bone marrow diseases or an enlarged spleen. Low WBC counts are also found in some cases of HIV infection.
As we have seen in previous sections, there are two primary types of WBC (leukocyte): a) those that stem from myeloid cells - and these include the granulocytes (basophils, mast cells, eosinophils, and neutrophils) and the monocytes (macrophages) - and b), those that stem from the lymphoid cells - and these comprise the lymphocytes (T-cells, B-cells and natural killer cells) - (See Fig. 1 - Sec 1.7.1).
The granulocytes (and monocytes) are the major phagocytic immune cells. Eosinophils and basophils may be increased in allergic conditions. Monocytes (macrophages) may be elevated following an infection or during a prolonged infection (they remove dead cells, organisms and other foreign particles from the blood). Neutrophils play a key role in the body's defence against invading bacteria. Someone with insufficient neutrophils is at risk for developing serious infections.
Lymphocytes play key roles in antibody production (i.e., B-cells > Plasma cells), and as generators of toxic, helper, suppressor and inducer cytokines (from T-cells) which have enormous influence over all kinds of leukocyte activity. Lymphocytes are especially important in fighting viral infections, like colds and flu. People with advanced HIV can have low lymphocyte counts, increasing their risk for developing certain infections. Also some medications (eg; cyclophosphamide) can decrease the number of white blood cells, which could therefore also increase your chances of getting an infection.
c) Platelets are cells that act to form a meshwork foundation barrier to help plug holes in your blood vessels following injury to prevent bleeding. They are the cellular foundation of blood clots and (eventually) scars.
High platelet blood values can occur in pregnancy or after strenuous exercise, cigarette smoking, excess production by the bone marrow or excessive blood loss.
Low values can also occur from premature destruction states such as Immune Thrombocytopenia (ITP), other autoimmune diseases (eg; where the effected individual produces an antibody to his or her own platelets), acute blood loss, drug effects (such as heparin: aspirin and some other medications make the platelets less "sticky”), infections with sepsis, entrapment of platelets in an enlarged spleen or bone marrow failure from diseases such as myelofibrosis or leukaemia. Some powerful arthritis medications in rare instances may also lower the platelet count. If the platelet count is too low, a person can be in danger of bleeding in any part of the body.
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Biopsy: A biopsy refers to a procedure that involves obtaining a tissue specimen for microscopic analysis to establish a precise diagnosis. Biopsies can be accomplished with a biopsy needle (passed through the skin into the organ in question) or by open surgical incision. (OMD)",
ANCA: Antineutrophil cytoplasmic antibodies (ANCAs) are autoantibodies directed against antigens found in cytoplasmic granules of neutrophiles and monocytes.
Antineutrophil cytoplasmic antibodies are closely associated with Wegener granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome and have contributed to new pathogenetic concepts and improved nomenclature of systemic vasculitides (antineutrophil cytoplasmic antibody-associated vasculitides)