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The ABCs of Blood Tests: Learn About Common Lab Tests Used to Detect Hematocrit Numbers, Cancer, Anemia and More

written by: Swagatam •edited by: lrohner•updated: 5/26/2011

Blood is the most important and life-defining component of our body, so it's no surprise it can also give us an indication of diseases that may be affecting us. Learn about some of the most common blood tests for adults and why they are so important.

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    Hematology

    The branch of science fundamentally engaged with the study and care of the overall well being of blood is called hematology. A hematological test may involve qualitative or quantitative examination of the formed elements of blood. This may include analyzing and acquiring data regarding blood cell morphology and/or counting the number of present leucocytes and erythrocytes. These tests greatly help to assess the general health conditions of the particular patient.

    One of the most common and regularly observed procedures inside a hematological laboratory is a CBC (Complete Blood Count) test. A CBC test may consist of the following combinations:

    • Red Blood Cell or RBC count
    • White Blood Cell or WBC count
    • Haemoglobin test
    • Haematocrit test
    • Red Blood Cell or RBC indices test
    • Differential count
    • Platelet number estimation
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    RBC Count Test

    An RBC Count helps to evaluate conditions like anemia and polyeythemia. Here, in a micro liter of blood the total erythrocyte count is determined.

    Procedure:

    • 5mL of whole blood (having EDTA) is received from the patient in a tube (lavender-top).
    • The sample is secured in a biohazard bag.
    • Through a standard practice, the RBC counting is done by an electronically controlled automated device.
    • The time, date and patient’s age are all recorded over a laboratory slip.

    Medical Implications:

    A reduced RBC count could possibly indicate the following abnormalities:

    Anemia: In this condition, usually there’s a decrease in the number of circulating erythrocytes, quantity of Hb or deflation of packed cells (Hct). An anemic patient may suffer from blood loss, self destruction of cells, and dietary insufficiency with certain vitamins and like iron responsible for enhancing RBC count.

    Other disorders may include:

    • Rheumatic fever
    • Lupus erythematosus
    • Myeloproliferative abnormality
    • Multiple myeloma
    • Leukemia
    • Hodgekin’s disease
    • Addison’s disease
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    WBC Count Test

    White blood cells are responsible for looking after the immunity of the body. Also called leukocytes, they fight infections and protect the body through a process called phagocytosis

    Leukocytes are also involved in the production and distribution of antibodies.

    Procedure:

    As done for RBC count test.

    Medical Implications:

    • If the WBC count is less than 4000/mm3 would point towards the following malfunctions:
    • High degree of bacterial or viral infection.
    • Hypersplenism
    • Depression of bone marrow due to toxic metal intake, radiation or harmful drugs.
    • Primary bone marrow disorder like leukemia, aplastic anemia, pernicious anemia.

    If there’s an increased WBC count, more than 11000/mm3 would generally indicate an increase in only a particular type of leukocyte. This condition is named as per the type of the cell that may show a typical increase:

    • Eosiniophilia
    • Basophilia
    • Neutrophelia
    • Monocytosis
    • Lymphocytosis
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    Hemoglobin Test (Hb)

    Healthy and abnormal conditions of hemoglobin are identified through electrophoresis.Here, the hemolyzed RBC substance is compared against the standard bands of many kind of known Hb.

    Commonly the forms of Hb a person normally may have are Hb A1, Hb F (fetal Hb) and among the many different types of abnormal Hb (also known as hemoglobinopathies), the popular ones are Hb S (leading to sickle test anemia) and Hb C (resulting in hemolytic anemia).However, the most common disorder is a substantial growth in Hb A2, indicating thalassemias, particularly a β-thalassemia characteristic.

    Significantly, there may be more than a 350 different varieties of Hb that has been found and investigated. Since it’s totally out of the scope of this article, would be difficult to elaborate any further on this.

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    Hematocrit Test (Hct) - Packed Cell Volume (PCV)

    Proceeding ahead from where we had left in the previous page, we’ll continue understanding blood test results and their implications through the following discussions – beginning with hematocrit test.

    Procedure:

    • 5ml of blood specimen is obtained from the patient through capillary puncture or finger puncture.
    • The capillary tube is filled up to 3/4rth of its volume with the blood specimen. The tube used is always a lavender-topped with EDTA.
    • The height of the packed cells is measured through a process of centrifugation inside a microcentrifuge machine. Here the plasma and the RBCs are separated from each other and hence the name hematocrit meaning “separation of blood."
    • After this the mass of RBC is measured indirectly and the results are recorded as volume percentage of the packed Red Blood Cells in whole blood (PCV).

    Medical Implications:

    With reference to the standard age specifications an increased hematocrit value would indicate severe dehydration, polycythemia, etc. and a decreased level would identify anemias and leukemias.

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    Red Cell Indices Test

    It defines the hemoglobim content of the RBC and also its size. It primarily includes:

    • Mean corpuscular hemoglobin concentration (MCHC)
    • Mean corpuscular volume (MCV)
    • Mean corpuscular hemoglobin (MCH)
    • The RBC indices is primarily used to differentiate anemias. When used along with the analysis of erythrocytes over a stained smear, a distinct RBC morphology may be certified.

    Procedure:

    As done for RBC test.

    Medical Implications:

    In deficient states of the RBC indices, the anemias may be distinguished by the cell size as:

    Microcytic, normocytic, macrocytic or microcytic hypochromie through cell size and color.

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    Platelet Number Estimation – Mean Platelet Volume (MPV)

    This value is used for evaluating bleeding disorders connected with thrombocytopenia, liver disease, uremia and for diagnosing diseases leading to bone marrow failure. MVP provides information regarding a proper balance of the platelet population size.

    Procedure:

    • 7mL of venous whole blood sample is obtained from the patient in a tube with lavender top and EDTA.
    • Counting of the platelets is done by an automated device or through phase microscopy.
    • The MVP is also counted through various instruments.
    • A blood smear is and the platelet size, shape and clumps are noted.
    • The specimen is secured inside a biohazard bag.

    Medical Implications:

    Increased numbers of platelets (thrombocytosis, thrombocythemia) would indicate the following abnormalities:

    • Chronic myelogenous
    • Polycythemia
    • Anemia with iron deficiency
    • Renal failure
    • Inflammatory diseases
    • Rheumatoid arthritis etc.

    Decreased numbers of platelets (thrombocytopenia) would indicate the following abnormalities:

    • Viral or bacterial infections
    • HIV infections
    • Alcohol abuse
    • Leukomias, myelofibrosis
    • Chemotherapy or radiation effects