complete blood count

Definition

A complete blood count (CBC) is a series of tests used to evaluate the composition and concentration of the cellular components of blood. It consists of the following tests: red blood cell (RBC) count, white blood cell (WBC) count, and platelet count; measurement of hemoglobin and mean red cell volume; classification of white blood cells (WBC differential); and calculation of hematocrit and red blood cell indices. The hematocrit is the percentage of blood by volume that is occupied by the red cells (i.e., the packed red cell volume). Red blood cell indices are calculations derived from the red blood cell count, hemoglobin, and hematocrit that aid in the diagnosis and classification of anemia.

Purpose

The CBC provides valuable information about the blood and to some extent the bone marrow, which is the blood-forming tissue. The CBC is used for the following purposes:

• as a preoperative test to ensure both adequate oxygen carrying capacity and hemostasis
• to identify persons who may have an infection
• to diagnose anemia
• to identify acute and chronic illness, bleeding tendencies, and white blood cell disorders such as leukemia
• to monitor treatment for anemia and other blood diseases
• to determine the effects of chemotherapy and radiation therapy on blood cell production

Precautions

The CBC requires a sample of blood collected from a vein. The nurse or phlebotomist inserting the needle should clean the skin first. The tourniquet should be removed from the arm as soon as the blood flows. If a fingerstick is used to collect the blood, care must be taken to wipe away the first drop, and not to squeeze the finger excessively as this causes the blood to be diluted by tissue fluid. Many drugs affect the results by causing increased or decreased RBC, WBC, and/or platelet production. Medications should be taken into account when interpreting results.

Description

The CBC is commonly performed on an automated hematology analyzer using well mixed whole blood that is added to a chemical called EDTA to prevent clotting. A CBC is a group of tests used to quantify the number of RBCs, WBCs, and platelets, provide information about their size and shape, measure the hemoblobin content of RBCs, determine the percentage and absolute number of the five white blood cell types, and identify early and abnormal blood cells. These tests are performed simultaneously, (usually in less than one minute), using an automated hematology analyzer. When the performance limit of the automated hematology analyzer is exceeded, sample dilution or pretreatment, manual smear review, or manual cell counts may be required. Each laboratory has established rules for determining the need for manual smear review based upon specific CBC parameters. For example, a manual differential is always performed when nucleated immature red blood cells are found on an electronic cell count.

Electronic Cell Counting

Electronic blood cell counting is based upon the principle of impedance (i.e., resistance to current flow). Some hematology analyzers combine impedance counting with light scattering to measure platelets. A small sample of the blood is aspirated into a chamber (the WBC counting bath) and diluted with a balanced isotonic saline solution that is free of particles. The diluted blood sample is split into two parts, one for counting RBCs and platelets and the other for counting WBCs. The RBC portion is transferred to the RBC/platelet counting bath where it is diluted further. The other portion remains in the WBC bath and a detergent (lysing agent) is added to destroy (hemolyze) the red blood cells. A small portion of the diluted fluid in each bath is allowed to flow past a small aperture. An electrical current is produced in each aperture by two electrodes, one on the inside and the other on the outside of the aperture. The saline solution is responsible for conducting current between the electrodes. The cells move through the aperture one at a time. When a cell enters the aperture, it displaces a volume of electrolyte equal to its size. The cell acts as an electrical resistor, and impedes the flow of current. This produces a voltage pulse, the magnitude of which is proportional to the size of the cell. Instrument electronics are adjusted to discriminate voltage pulses produced by different cells. These adjustments are called thresholds. For example, the threshold for counting a RBC is equivalent to a cell volume of 36 femtoliters or higher. Voltage pulses that are equivalent to volumes of 2–20 femtoliters are counted as platelets. This process is repeated two more times so that the RBC, WBC, and platelet counts are performed in triplicate. Each time frame for counting is several seconds and many thousands of cells are counted. The computer processes the counting data first by determining the agreement between the three counts. If acceptable criteria are met, the counts are accepted and used to calculate the result.

The hemoglobin concentration is measured optically using the solution in the WBC bath. The lysing agent contains potassium cyanide that reacts with the hemoglobin to form cyanmethemoglobin. The optical density of the cyanmethemoglobin is proportional to hemoglobin concentration.

The voltage pulses produced by the white blood cells depend upon the size of the cell and its nuclear density. Therefore, the pulses may be analyzed to differentiate between the types of WBCs found. For example, lymphocytes are the smallest WBCs and comprise the lower end of the size scale. Monocytes, prolymphocytes, and immature granulocytes comprise the central area of the WBC histogram, and mature granulocytes comprise the upper end. In addition to cell sizing, automated instruments may use any of three other methods to distinguish between subpopulations. These are radio frequency conductance, forward and angular light scattering, and fluorescent staining.

Red Blood Cell Count

The red cells, the most numerous of the cellular elements, carry oxygen from the lungs to the body's tissues. They are released from the bone marrow into the blood in an immature form called the reticulocyte that still retains much of the cellular RNA needed for hemoglobin production. Reticulocytes may be counted on some automated analyzers and are an index to recovery from anemia. The average life span of RBCs in the circulation is approximately 120 days.

The red blood cell (RBC) count determines the total number of red cells (erythrocytes) in a sample of blood. Most anemias are associated with a low RBC count, hemoglobin, and hematocrit. Common causes include excessive bleeding; a deficiency of iron, vitamin B₁₂, or folic acid; destruction of red cells by antibodies or mechanical trauma; bone marrow malignancy and fibrosis; and structurally abnormal hemoglobin. The RBC count is also decreased due to cancer, kidney diseases, and excessive IV fluids. An elevated RBC count may be caused by dehydration, hypoxia (decreased oxygen), or a disease called polycythemia vera. Hypoxia may result from high altitudes, chronic obstructive lung diseases, and congestive heart failure.

Hematocrit and Cell Indices

The hematocrit is a test that measures the volume of blood in percent that is comprised of the red blood cells. Automated cell counters calculate the hematocrit by multiplying the RBC count by the mean red cell volume. A decrease in the number or size of red cells also decreases the amount of space they occupy, resulting in a lower hematocrit. Conversely, an increase in the number or size of red cells increases the amount of space they occupy, resulting in a higher hematocrit. Thalassemia minor, a genetic cause of anemia, is an exception in that it usually causes an increase in the number of red blood cells, but because they are small, it results in a decreased hematocrit.

The three main RBC indices are used to determine the average size and hemoglobin content of the RBCs and they help determine the cause of anemia. The three indices are described below:

• Mean corpuscular volume (MCV)—the average size of the red blood cells expressed in femtoliters. MCV is calculated by dividing the hematocrit (as percent) by the RBC count in millions per microliter of blood, then multiplying by 10.
• Mean corpuscular hemoglobin (MCH)—the average amount of hemoglobin inside an RBC expressed in picograms. The MCH is calculated by dividing the hemoglobin concentration in grams per deciliter by the RBC count in millions per microliter, then multiplying by 10.
• Mean corpuscular hemoglobin concentration (MCHC)—the average concentration of hemoglobin in the RBCs expressed in percent. It is calculated by dividing the hemoglobin in grams per deciliter by the hematocrit, then multiplying by 100.

The mechanisms by which anemia occurs will alter the RBC indices in a predictable manner. Therefore, the RBC indices permit the physician to narrow down the possible causes of an anemia. The MCV is an index of the size of the RBCs. When the MCV is below normal, the RBCs will be smaller than normal and are described as microcytic. When the MCV is elevated, the RBCs will be larger than normal and are termed macrocytic. RBCs of normal size are termed normocytic. Failure to produce hemoglobin results in smaller than normal cells. This occurs in many diseases including iron deficiency anemia, thalassemia (an inherited disease in which globin chain production is deficient), and anemias associated with chronic infection or disease. Macrocytic cells occur when division of RBC precursor cells in the bone marrow is impaired. The most common causes of macrocytic anemia are vitamin B₁₂ deficiency, folate deficiency, and liver disease. Normocytic anemia may be caused by decreased production (e.g., malignancy and other causes of bone marrow failure), increased destruction (hemolytic anemia), or blood loss. The RBC count is low, but the size and amount of hemoglobin in the cells is normal.

White Blood Cell Count

The majority of CBCs include both a WBC count and an automated differential. A differential determines the percentage of each of the five types of mature white blood cells. An elevated WBC count occurs in infection, allergy, systemic illness, inflammation, tissue injury, and leukemia. A low WBC count may occur in some viral infections, immunodeficiency states, and bone marrow failure. The WBC count provides clues about certain illnesses, and helps physicians monitor a patient's recovery from others. The differential will reveal which WBC types are affected most. For example, an elevated WBC count with an absolute increase in lymphocytes having an atypical appearance is most often caused by infectious mononucleosis. The differential will also identify early WBCs that may be reactive (e.g., a response to acute infection) or the result of a leukemia.

When the electronic WBC count is abnormal or a cell population is flagged, meaning that one or more of the results is atypical, a manual differential is performed. In that case, a wedge smear is prepared. This is done by placing a drop of blood on a glass slide, and using a second slide to pull the blood over the first slide's surface. The smear is air dried, then stained with Wright stain and examined under a microscope using oil immersion (1000x magnification). One hundred white cells are counted and identified as either neutrophils, lymphocytes, monocytes, eosinophils, or basophils based on the shape and appearance of the nucleus, the color of cytoplasm, and the presence and color of granules. The purpose is to determine if these cells are present in a normal distribution, or if one cell type is increased or decreased. Any atypical or immature cells also are counted.

In addition to determining the percentage of each mature white blood cell, the following tests are performed as part of the differential:

• Evaluation of RBC morphology is performed. This includes grading of the variation in RBC size (anisocytosis) and shape (poikioocytosis); reporting the type and number of any abnormal RBCs such as target cells, sickle cells, stippled cells, etc.; reporting the presence of immature RBCs (polychromasia); and counting the number of nucleated RBCs per 100 WBCs.
• An estimate of the WBC count is made and compared to the automated or chamber WBC count. An estimate of the platelet count is made and compared to the automated or chamber platelet count. Abnormal platelets such as clumped platelets or excessively large platelets are noted on the report.
• Any immature white blood cells are included in the differential count of 100 cells, and any inclusions or abnormalities of the WBCs are reported.

WBCs consist of two main subpopulations, the mononuclear cells and the granulocytic cells. Mononuclear cells include lymphocytes and monocytes. Granulocytes include neutropohils (also called polymorphonuclear leukocytes or segmented neutrophils), eosinophils, and basophils. Each cell type is described below:

• Neutrophils are normally the most abundant WBCs. They measure 12–16 μm in diameter. The nucleus stains dark purple-blue, and is divided into several lobes (usually three or four) consisting of dense chromatin. A neutrophil just before the final stage of maturation will have an unsegmented nucleus in the shape of a band. These band neutrophils may be counted along with mature neutrophils or as a separate category. The cytoplasm of a neutrophil contains both primary (azurophilic) and secondary (specific) granules. The secondary granules are lilac in color and are more abundant, almost covering the pink cytoplasm. Neutrophils are phagocytic (able to engulf objects) cells and facilitate removal of bacteria and antibody-coated antigens. The neutrophilic granules are rich in peroxidase, and aid the cell in destroying bacteria and other ingested cells.
• Eosinophils are 14–16 μm in diameter and contain a blue nucleus that is segmented into two distinct lobes. The cytoplasm is filled with large refractile orange-red granules. The granules contain peroxidase, hydrolases, and basic proteins that aid in the destruction of phagocytized cells. Eosinophils are increased in allergic reactions and parasitic infections.
• Basophils, like eosinophils, are 14–16 μm in diameter and have a blue nucleus that is bilobed. The cytoplasm of the basophil is filled with large dark blue-black granules that may obscure the nucleus. These contain large amounts of histamine, heparin, and acid mucopolysaccharides. Basophils mediate the allergic response by releasing histamine.
• Lymphocytes are the second most abundant WBCs. They may be small (7–9 μm in diameter) or large (12–16 μm in diameter). The nucleus is dark blue and is nearly round or slightly indented and the chromatin is clumped and very dense. The cytoplasm is medium blue and usually agranular. An occasional lymphocyte will have a few azurophilic granules in the cytoplasm. Lymphocytes originate in the lymphoid tissues and are not phagocytic. They are responsible for initiating and regulating the immune response by the production of antibodies and cytokines.
• Monocytes are the largest WBCs, measuring 14–20 μm in diameter. They have a large irregularly shaped and folded blue nucleus with chromatin that is less dense than other WBCs. The cytoplasm is gray-blue, and is filled with fine dust-like lilac colored granules. Monocytes are phagocytic cells that process and present antigens to lymphocytes, an event required for lymphocyte activation.

Platelet Count

Platelets are disk-shaped structures formed by the detachment of cytoplasm from megakaryocytes. They aid in the coagulation process by attaching or adhering to the walls of injured blood vessels, where they stick together to form the initial platelet plug. A low platelet count may occur in patients with AIDS, viral infections, lymphoma, and lupus erythematosus, or in patients taking certain drugs, most notably quinine and quinidine. Decreased platelet production is also a cause of thrombocytopenia, and may be due to aplastic anemia, leukemia, lymphoma, or bone marrow fibrosis. A low platelet count can occur due to increased destruction. This can result from antibody production that is often drug-induced (heparin treatment being a prominent cause). Increased destruction also results from autoantibody production as occurs in idiopathic thrombocytopenic purpura (ITP) and thrombotic episodes that consume platelets such as occur in thrombotic thrombocytopenic purpura (TTP), disseminated intravascular coagulation (DIC), and hemolytic-uremic syndrome (HUS). Inherited (congenital) thrombocytopenia can be caused by Glanzmann's thrombasthenia, Fanconi syndrome, and Wiskott-Aldrich syndrome.

Thrombocytosis, an increased platelet count, is most often caused by a reaction to injury or inflammation. In these cases the platelet count increases transiently and is usually within the range of 400,000–800,000 per microliter. Persistent or higher counts are usually associated with myeloproliferative disease (malignant disease involving blood forming cells) such as chronic granulocytic (myelogenous) leukemia, polycythemia vera, or primary (essential) thrombocythemia.

The platelet count is most often measured by impedance counting but is performed manually when the platelet count is very low, platelet clumping is observed, or abnormally large (giant) platelets are present. Often these abnormalities and others such as cryoglobulinemia, cell fragmentation (hemolysis), and microcytic RBCs are signaled by abnormal RBC and platelet indices and abnormal population flags. An abnormal mean platelet volume or platelet histogram indicates that morphological platelet abnormalities are present and the platelets should be observed from a stained blood film to characterize the abnormality. The platelet count can be estimated using the Wright-stained blood smear used for a differential WBC count by multiplying the average number of platelets per oil immersion field by 20,000. Platelet estimates should correlate with actual counts. When they disagree, the platelet count should be repeated and a manual count performed if necessary.

Preparation

The CBC does not require fasting or any special preparation.

Aftercare

Discomfort or bruising may occur at the puncture site. Applying pressure to the puncture site until the bleeding stops helps to reduce bruising; warm packs relieve discomfort. Some people feel dizzy or faint after blood has been drawn and should be treated by resting awhile.

Risks

Other than potential bruising at the puncture site, and/or dizziness, there are no complications associated with this test.

Normal Results

CBC values vary by age and sex. Normal values are ultimately determined by the laboratory performing the test. As a guide, the normal values for men and nonpregnant women are as follows:

• WBCs: 4,500–11,000 per microliter for women and men, with neutrophils representing 50–70%, lymphocytes 25–35%, monocytes 4–6%, eosinophils 1–3%, basophils 0.4–1%, and bands 0–5%.
• RBCs: 4.2–5.0 million per microliter for women; 4.5–6.2 million per microliter for men.
• Hemoglobin: 12–15 g/dL for women; 13.6–17.2 g/dL for men.
• Hematocrit: 35–47% for women; 42–52% for men.
• Platelets: 150,000 and 350,000 per microliter.
• Reticulocyte count: 0.5–1.5%.

Normal adult results for red blood cell indices are as follows:

• MCV: 80–98 fl (femtoliters)
• MCHC: 32–36%
• MCH: 27–31 pg (picograms)
• RDW: 11.5–14.5%

In addition to normal values, critical values (alert, panic values) are established for hemoglobin (and hematocrit), WBC count, and platelet count. Precipitously low hemoglobin is associated with hypoxia that can have life-threatening complications. Extremely low WBCs indicates an inability to fight infection and a high risk of sepsis. A severely reduced platelet count predisposes the patient to spontaneous internal bleeding. Representative critical values are shown below.

• Hemoglobin: less than 5.0 g/dL
• Hematocrit: less than 15%
• Platelet count: less than 30,000 per microliter
• WBC count: less than 2,500 per microliter and greater than 30,000 per microliter

Abnormal blood count results are seen in a variety of conditions. One of the most common is anemia, which is characterized by a low RBC count, hemoglobin, and hematocrit. The category into which a person's anemia is placed is in part based upon the red blood cell indices provided. The indices provide a significant clue as to the cause of the anemia, but further testing is needed to confirm a specific diagnosis. The most common causes of macrocytic anemia (high MCV) are vitamin B₁₂ and folic acid deficiencies. Lack of iron in the diet, thalassemia (a type of hereditary anemia), and chronic illness are the most common causes of microcytic anemia (low MCV). Normocytic anemia (normal MCV) can be caused by kidney and liver disease, bone marrow disorders, leukemia, excessive bleeding, or hemolysis of the red blood cells. Iron deficiency and thalassemia are the most common causes of hypochromic anemia (low MCHC). Normocytic anemias are usually also normochromic and share the same causes. The red cell distribution width (RDW) is increased in anemias caused by deficiencies of iron, vitamin B₁₂, or folic acid. Abnormal hemoglobins, such as in sickle cell anemia, can change the shape of red blood cells as well as cause them to hemolyze, or rupture. The abnormal shape and the cell fragments resulting from hemolysis increase the RDW. Conditions that cause more immature cells to be released into the bloodstream, such as severe blood loss, will increase the RDW. The larger size of immature cells creates a distinct size variation.

Infections and leukemias are associated with increased numbers of WBCs. Increases or decreases in the percentage of each white cell can be associated with a number of diseases or conditions, including cancer, leukemia, anemia, multiple sclerosis, allergies, parasitic and viral diseases, infections, and tissue damage.

Resources

Books

Chernecky, Cynthia C. and Barbara J. Berger. Laboratory Tests and Diagnostic Procedures. 3rd ed. Philadelphia, PA: W. B. Saunders, 2001.

Henry, John B. Clinical Diagnosis and Management by Laboratory Methods. Philadelphia: W. B. Saunders, 2001.

Kee, Joyce LeFever. Handbook of Laboratory and DiagnosticTests. 4th ed. Upper Saddle River, NJ: Prentice Hall, 2001.

Wallach, Jacques. Interpretation of Diagnostic Tests. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2000.

— Victoria E. DeMoranville Mark A. Best

(1) (Cell Broadcast Center) See cell broadcast.

(2) (Cipher Block Chaining) In cryptography, a mode of operation that combines the ciphertext of one block with the plaintext of the next block. The problem of repeating ciphertext that results from the electronic code book method is eliminated. See mode of operation, block cipher and CBC-MAC.

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The determination of the number of red blood cells (erythrocytes), white blood cells, and platelets in an accurately measured volume of blood. It usually includes the quantity of hemoglobin per cubic millimeter of blood. A normal red blood count is 4 to 5.5 million cells/cubic mm of blood.

The clinical laboratory test that evaluates the three main cellular components of peripheral blood (red cells, white cells, and platelets) is called the "complete blood count" (CBC). It is used commonly to assess whether a patient is anemic (low red cell count), has an infection (increased white blood cells), or has abnormal blood coagulation (platelet levels). The CBC examines the total number of red blood cells (RBC) and the RBC indices, including: the mean corpuscular volume (MCV); the concentration of hemoglobin, measured by the mean corpuscular hemoglobin (MCH) and its concentration (MCHC); and the hematocrit, which is the mean packed-cell volume of red cells. The total white blood cell (leukocyte) count, the various types of leukocytes (lymphocytes, monocytes, neutrophils, eosinophils, and basophils), and platelets are also measured.

(SEE ALSO: Hematocrit; Hemoglobin; Laboratory Services)

— JONATHAN R. KELLER; MARIAESTELA ORTIZ

A measure of the composition of blood. It includes haemoglobin concentration and white blood cell count.

Complete blood (cell) count. See also blood count.

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2007)

Schematics (also sometimes called "Fishbones") of shorthand for complete blood count commonly used by clinicians and healthcare providers. The shorthand on the right is used more often in the US. Hgb=Hemoglobin, WBC=White blood cells, Plt=Platelets, Hct=Hematocrit.

A complete blood count (CBC), also known as full blood count (FBC) or full blood exam (FBE) or blood panel, is a test requested by a doctor or other medical professional that gives information about the cells in a patient's blood. A scientist or lab technician performs the requested testing and provides the requesting medical professional with the results of the CBC.

Alexander Vastem is widely regarded as being the first person to use the complete blood count for clinical purposes.^{[citation needed]} Reference ranges used today stem from his clinical trials in the early 1960s.

The cells that circulate in the bloodstream are generally divided into three types: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes). Abnormally high or low counts may indicate the presence of many forms of disease, and hence blood counts are amongst the most commonly performed blood tests in medicine, as they can provide an overview of a patient's general health status. A CBC is routinely performed during annual physical examinations in some jurisdictions.

Contents 1 Methods 1.1 Samples 1.2 Automated blood count 1.3 Manual blood count 2 Results 2.1 Red cells 2.2 White cells 2.3 Platelets 3 Interpretation 4 References

Methods

Samples

A phlebotomist collects the specimen, in this case blood is drawn in a test tube containing an anticoagulant (EDTA, sometimes citrate) to stop it from clotting, and transported to a laboratory.

In the past, counting the cells in a patient's blood was performed manually, by viewing a slide prepared with a sample of the patient's blood under a microscope (a blood film, or peripheral smear). Nowadays, this process is generally automated by use of an automated analyzer, with only approximately 30% samples now being examined manually.

Automated blood count

Complete blood count performed by an automated analyser. Differentials missing.

The blood is well mixed (though not shaken) and placed on a rack in the analyzer. This instrument has many different components to analyze different elements in the blood. The cell counting component counts the numbers and types of different cells within the blood. The results are printed out or sent to a computer for review.

Blood counting machines aspirate a very small amount of the specimen through narrow tubing. Within this tubing, there are sensors that count the number of cells going through it, and can identify the type of cell; this is flow cytometry. The two main sensors used are light detectors, and electrical impedance. One way the instrument can tell what type of blood cell is present is by size. Other instruments measure different characteristics of the cells to categorize them.

Because an automated cell counter samples and counts so many cells, the results are very precise. However, certain abnormal cells in the blood may be identified incorrectly, and require manual review of the instrument's results and identifying any abnormal cells the instrument could not categorize.

In addition to counting, measuring and analyzing red blood cells, white blood cells and platelets, automated hematology analyzers also measure the amount of hemoglobin in the blood and within each red blood cell. This information can be very helpful to a physician who, for example, is trying to identify the cause of a patient's anemia. If the red cells are smaller or larger than normal, or if there's a lot of variation in the size of the red cells, this data can help guide the direction of further testing and expedite the diagnostic process so patients can get the treatment they need quickly.

Automated blood counting machines include the Medonic M Serise,Beckman Coulter LH series, Roche Sysmex XE-2100, Siemens ADVIA 120 & 2120, the Abbott Cell-Dyn series,and the Mindray BC series.

Manual blood count

Counting chambers that hold a specified volume of diluted blood (as there are far too many cells if it is not diluted) are used to calculate the number of red and white cells per litre of blood.

To identify the numbers of different white cells, a blood film is made, and a large number of white cells (at least 100) are counted. This gives the percentage of cells that are of each type. By multiplying the percentage with the total number of white blood cells, the absolute number of each type of white cell can be obtained.

The advantage of manual counting is that automated analysers are not reliable at counting abnormal cells. That is, cells that are not present in normal patients and are only seen in the peripheral blood with certain haematological conditions. Manual counting is subject to sampling error because so few cells are counted compared with automated analysis.

30% of CBCs have medical scientists manually looking at a blood film down the microscope, not only to find abnormal white cells, but also because variation in the shape of red cells is an important diagnostic tool. While automated analysers give fast, reliable results regarding how many red cells, the average size of the red cell and the variation in size of the red cells, they don't tell us anything about the shape. Also, a percentage of normal patient's platelets will clump in EDTA anticoagulated blood. In these cases the automatic analysers will give a falsely lower platelet count. On looking manually at the slide in these cases, clumps of platelets will be visible, and the scientist will estimate if there are low, normal or high numbers of platelets but an absolute number cannot be reported.

Results

For examples of standard values, see Reference ranges for blood tests#Hematology.

A scanning electron microscope (SEM) image of normal circulating human blood. One can see red blood cells, several knobby white blood cells including lymphocytes, a monocyte, a neutrophil, and many small disc-shaped platelets.

A complete blood count will normally include:

Red cells

• Total red blood cells - The number of red cells is given as an absolute number per litre.
• Hemoglobin - The amount of hemoglobin in the blood, expressed in grams per decilitre. (Low hemoglobin is called anemia.)
• Hematocrit or packed cell volume (PCV) - This is the fraction of whole blood volume that consists of red blood cells.
• Red blood cell indices
  • Mean corpuscular volume (MCV) - the average volume of the red cells, measured in femtolitres. Anemia is classified as microcytic or macrocytic based on whether this value is above or below the expected normal range. Other conditions that can affect MCV include thalassemia and reticulocytosis.
  • Mean corpuscular hemoglobin (MCH) - the average amount of hemoglobin per red blood cell, in picograms.
  • Mean corpuscular hemoglobin concentration (MCHC) - the average concentration of hemoglobin in the cells.
• Red blood cell distribution width (RDW) - a measure of the variation of the RBC population

White cells

• Total white blood cells - All the white cell types are given as a percentage and as an absolute number per litre.

A complete blood count with differential will also include:

• Neutrophil granulocytes - May indicate bacterial infection. May also be raised in acute viral infections.Because of the segmented appearance of the nucleus, neutrophils are sometimes referred to as "segs." The nucleus of less mature neutrophils is not segmented, but has a band or rod-like shape. Less mature neutrophils - those that have recently been released from the bone marrow into the bloodstream - are known as "bands" or "stabs". Stab is a German term for rod.[1]
• Lymphocytes - Higher with some viral infections such as glandular fever and. Also raised in lymphocytic leukaemia CLL. Can be decreased by HIV infection. In adults, lymphocytes are the second most common WBC type after neutrophils. In young children under age 8, lymphocytes are more common than neutrophils.[2].
• Monocytes - May be raised in bacterial infection, tuberculosis, malaria, Rocky Mountain spotted fever, monocytic leukemia, chronic ulcerative colitis and regional enteritis [3]
• Eosinophil granulocytes - Increased in parasitic infections, asthma, or allergic reaction.
• Basophil granulocytes- May be increased in bone marrow related conditions such as leukemia or lymphoma. [4]

A manual count will also give information about other cells that are not normally present in peripheral blood, but may be released in certain disease processes.

Platelets

• Platelet numbers are given, as well as information about their size and the range of sizes in the blood.

Interpretation

Certain disease states are defined by an absolute increase or decrease in the number of a particular type of cell in the bloodstream. For example:

Type of Cell	Increase	Decrease
Red Blood Cells (RBC)	erythrocytosis or polycythemia	anemia or erythroblastopenia
White Blood Cells (WBC):	leukocytosis	leukopenia
-- lymphocytes	-- lymphocytosis	-- lymphocytopenia
-- granulocytes:	-- granulocytosis	-- granulocytopenia or agranulocytosis
-- --neutrophils	-- --neutrophilia	-- --neutropenia
-- --eosinophils	-- --eosinophilia	-- --eosinopenia
-- --basophils	-- --basophilia	-- --basopenia
Platelets	thrombocytosis	thrombocytopenia
All cell lines	-	pancytopenia

Many disease states are heralded by changes in the blood count:

• leukocytosis can be a sign of infection.
• thrombocytopenia can result from drug toxicity.
• pancytopenia is generally as the result of decreased production from the bone marrow, and is a common complication of cancer chemotherapy.

References

• http://www.missouricancer.com/index.jsp?page=cbc
• http://www.labtestsonline.org/understanding/analytes/cbc/test.html

v • d • e Medical test: Serology, reference range: blood tests Clinical biochemistry Metabolic panel BMP: electrolytes (Na+/K+, Cl-/HCO3-) · renal function, BUN-to-creatinine ratio (BUN/Creatinine) · Glucose · Ca CMP: BMP + protein tests (Human serum albumin, Serum total protein) · liver function tests (ALP, ALT, AST, Bilirubin) derived values: Plasma osmolality · Serum osmolal gap Acid-base homeostasis Arterial blood gas · Base excess · Anion gap · CO2 content Iron tests Transferrin saturation = Serum iron / Total iron-binding capacity Ferritin · Transferrin · Transferrin receptor Blood sugar Glucose test · Glucose tolerance test · Glycemia · Noninvasive glucose · C-peptide · Fructosamine · Random glucose test · Glycosylated hemoglobin Endocrine ACTH stimulation test · Thyroid function tests Cardiac marker Troponin test · CPK-MB test · Glycogen phosphorylase isoenzyme BB Other Beutler test · Blood lipids · Tumor marker Hematology/CBC Clotting vWF: Ristocetin induced platelet agglutination clotting factors: Prothrombin time · Partial thromboplastin time · Thrombin time other/general coagulation: Bleeding time · animal enzyme (Reptilase time, Ecarin clotting time, Dilute Russell's viper venom time) · Thromboelastography fibrinolysis: Euglobulin lysis time · D-dimer Red blood cell indices Hematocrit · Hemoglobin · RBC count ratios: Mean corpuscular hemoglobin · Mean corpuscular hemoglobin concentration · Mean corpuscular volume Fetal hemoglobin: Apt-Downey test · Kleihauer-Betke test · Red blood cell distribution width Reticulocyte index · Haptoglobin Other Blood film · Blood viscosity · Absolute neutrophil count Immunology Infections viral infection: HIV (HIV test, BDNA test) · Epstein-Barr virus (Monospot test) bacterial infection: syphilis (VDRL, Rapid plasma reagin, Wassermann test, FTA-ABS) · rickettsia (Weil-Felix test) · helicobacter (HelicoCARE direct) · streptococcus (Antistreptolysin O titre) protozoan infection: toxoplasmosis (Sabin-Feldman dye test) Inflammation C-reactive protein · Erythrocyte sedimentation rate · MELISA · RAST test see also reference ranges for blood tests

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