CBC Basics

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CBC Basics

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6/9/2010

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The complete blood count (CBC) includes the white blood cell (WBC)

count, red blood cell (RBC) count, hemoglobin, hematocrit, platelet

count, white blood cell differential, and red blood cell indices. Thereticulocyte count is also included because it is closely related to the

CBC. The WBC differential is the classification, either automated or

manually performed by a technologist, of the white blood cells. Both

the red blood cells and the white blood cells are also visually scanned

for abnormalities if the automated results indicate the need. Cells are

also counted and identified in sources such as cerebrospinal fluid

(CSF), urine, and various other body fluids.

Hematopoiesis

It is helpful to understand the basics of cellular formation in the

human body in order to understand the value of the complete blood

count in diagnosing and monitoring disease states. There are three

types of cellular elements present in circulating blood: erythrocytes

(red blood cells, RBC), leukocytes (white blood cells, WBC), and

thrombocytes (platelets). In a healthy individual, the destruction and

production of each cell type is constant. Hematopoiesis is the term

which meansproduction of blood cells

Cells go through various stages as they become mature and are

able to carry out their designated functions. Normally, only the

mature stages of the cells are found in the peripheral blood. In

disease states, immature and abnormal forms of the various cells may

be found. These immature and abnormal cells are noted by the

automated instrumentation in the laboratory, but the technologist

must make the final decision as to the type of cell present. The


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technologist relies on his/her knowledge and experience to properly

identify the type of immature or abnormal cells found in a patients

blood. Slides of the patients blood are made, stained, and individually

studied microscopically. If the technologist questions the identification

of a cell, he/she refers the slide to the pathologist who makes the final

decision.

Before a baby is born, hematopoiesis takes place in the liver,

spleen, thymus, bone marrow, and lymph nodes. Only two weeks

after a baby is conceived, a type of red blood cell is formed in the yolk

sac. By the second month of gestational life, some leukocytes and

megakaryocytes (which form platelets) appear, and the liver and

spleen take over the function of producing cells. By the fifth month in

his/her mothers womb, the bone marrow has taken over the primary

role of hematopoesis.

Blood cells arise from hematopoietic stem cell in the bone

marrow. (These cells can repopulate the bone marrow after injury or

irradiation, which is the theory behind bone marrow transplants.)

These stem cells are thought to differentiate into red cells, various

white cell types, and platelets. These cells transform from the

primitive blast stage into the various stages of each type of cell in a

gradual manner; this often makes it difficult to absolutely state the

level of maturation of a cell seen on a blood smear. As a cell matures,

there are changes in the cytoplasm, nucleus, and cell size.

The CBC is often used in preoperative laboratory work because it

tells much about a patients health. The WBC count is one of the firstparameters affected when a persons health is not optimum. If a

patients WBC count is not normal, then the health care practitioner is

given a direction to take in administering medical advice and/or

medication.


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The White Blood Cell Count

White blood cells, or leukocytes, are reported as the number of

cells per cubic millimeter (cumm) of whole blood, or as the number of

cells per microliter (ul) since a cumm is equal to a ul. A microliter is 1

x 10^(-6) liter. The normal WBC varies depending on the age of the

patient. The WBC is a good indicator of many disease states, and it is

often monitored during various therapies. It may be increased in

bacterial infections, pregnancy, and a variety of other conditions. It

may be decreased in other conditions such as hepatitis, cirrhosis of the

liver, rheumatoid arthritis, and lupus erythematosus. Leukemia may

cause the WBC to be either increased or decreased, depending on the

type and stage of the leukemia. In chemo and radiation therapy, the

WBC can drop drastically low as a result of the cells being killed. If the

WBC is too low, the patients immune system cannot work properly,

and the patient is at risk of serious infection.

The term leukocytosis refers to an increase of white blood cells

above normal, and the term leukopeniarefers to a decrease of white

blood cells below normal. The WBC count responds to illness, but it

also fluctuates somewhat with exercise, stress, and anxiety. In

children, the WBC count may respond more quickly than in adults, and

their count may elevate rapidly with infection.

The Red Blood Cell Count

The red blood cells, or erythrocytes, are reported as the number

of cells per microliter of whole blood. The normal RBC varies

according to age and gender, and somewhat to physical exercise and


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daily fluctuations. The RBC count is increased in a few disease states

and in conditions such as dehydration and increase in altitude. More

significantly, however, is the decrease in the RBC count due to

anemia, bleeding, and many other disorders.

As in the WBC count, care must be taken to send a good

specimen to the laboratory for analysis. Clots greatly affect the

accuracy of the RBC count, artificially decreasing the count which

indicates a disease state that the patient may not actually have. This

may mislead to the misdiagnosing the patient and subsequently

offering the wrong treatment to the patient.

The RBC count is also often used in preoperative laboratory work

because it can indicate if a patient is physiologically strong enough to

undergo surgery. An abnormal RBC count may indicate an underlying

cause of a symptom, or it may be the symptom of an underlying

cause.

Hemoglobin

Hemoglobin is the major parameter used in diagnosing and

monitoring anemia and polycythemia. It is reported as grams/deciliter

(dl) of whole blood. The normal hemoglobin value varies with age and

gender, and there is slight variation throughout the day, with exercise,

and with altitude.

The main function of the RBC is to synthesize hemoglobin.

Hemoglobin is used to carry oxygen to tissues and to bring carbondioxide from the tissues to the lungs. The hemoglobin molecule is

composed of four sub-units, each containing heme and the protein

globin. Every hemoglobin molecule is able to transport four moles of

oxygen. An atom of iron is located in the center of the structure and


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binds to the oxygen. Iron is carried to the RBC by a blood plasma

protein called transferrin. Most of this iron is used in the synthesis of

heme.

There are three types of hemoglobin found in the normal adult

hemoglobin A, F, and A2. Hemoglobin A makes up approximately 95-

98% of the total, while HgbF makes up approximately 2%, and A2, 2-

3%. The type of polypeptide chains that make up the molecule

determines the type of hemoglobin. One heme group is attached to

each polypeptide chain, linked by the iron in the heme group. The

mature red blood cell consists mainly of hemoglobin. However, the

production of heme and globin occurs mainly in the immature red

blood cell.

Abnormal hemoglobin variants create symptoms that occur in

cases such as sickle cell anemia (HgbS) and hemolytic anemia (HgbC).

Hematocrit

The hematocrit is simply the percentage of red blood cells towhole blood. When anticoagulated whole blood is centrifuged, the

erythrocytes, leukocytes, and platelets will be forced to the bottom of

the sample. The heaviest cells (the RBCs) will go farthest to the

bottom of the tube, followed by a thin layer of WBCs and finally the

platelets on top. The liquid portion on top is calledplasma. The

volume of erythrocytes is also called thepacked red cell volume (PCV),

and it is expressed as a percentage of the total whole blood volume.The hematocrit can be measured by actual percentage after

centrifuging a small capillary tube of whole blood, or it can be

performed by automated methods.


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Like the hemoglobin, the hematocrit is used to monitor anemic

conditions. It is decreased in anemia and increased in forms of

polycythemia. .

Reticulocyte Count

Reticulocyte count is a test used to determine how the bone

marrow is responding to the bodys need for RBCs. The reticulocyte is

the erythrocyte prior to becoming a mature RBC. The erythrocyte

passes through 6 stages of development, the first four stages normally

occurring only in the bone marrow: pronormoblast, basophilicnormoblast, polychromatophilic normoblast, orthochromic normoblast,

reticulocyte, and mature erythrocyte. Three to four mitotic divisions

occur between the pronormoblast and the polychromatophilic

normoblast, producing up to 16 erythrocytes from each

pronormoblast. About three days lapse between the pronormoblast

stage and the orthochromic normoblast stage. This latter stage still

contains the nucleus, though it is very condensed and incapable offurther mitosis. On about the fourth day from the pronormoblast

stage, the nucleus is extruded from the cell and a reticulocyte is

formed. Reticulocytes are slightly larger than mature erythrocytes.

They stay in the bone marrow for 2 3 more days and are then

released into the peripheral blood where they age for an additional day

before becoming mature red blood cells.

When a persons hemoglobin drops below normal, the oxygencontent of the blood drops and the oxygen tension in the kidneys is

reduced. This stimulates the kidneys to increase their production of

erythropoietin, a hormone that initiates production of red blood cells.

An increased number of red blood cells are then produced and the rate


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of mitosis is increased, thus causing the maturation process in the

bone marrow to shorten, creating a shorter life span for the

reticulocyte in the bone marrow, which results in an increased

reticulocyte count.

The reticulocyte count thus reflects the amount of red blood cell

production taking place in the bone marrow. The normal life span of a

mature erythrocyte is 120 days, +/- 20 days, which means the bone

marrow replaces approximately 1% of the adult red blood cells daily.

The normal reticulocyte count is therefore 0.5 1.5 %. A decreased

reticulocyte count occurs in conditions in which the bone marrow is not

producing erythrocytes, such as aplastic anemia, iron deficiency

anemia, or cancer. Increased reticulocyte counts occur in hemolytic

anemias, iron deficient anemias involving iron therapy, thalassemia,

blood loss (acute and chronic), and other anemias and during

pregnancy. Newborns will have an increased reticulocyte count, but

drops within weeks after birth.

Red Blood Cell Indices

Red blood cell indices are calculated values used to help

determine the size and hemoglobin content of the red blood cells.

They can be helpful in diagnosing and differentiating anemias. The

indices are the MCV (mean corpuscular volume), MCH (mean

corpuscular hemoglobin), and MCHC (mean corpuscular hemoglobin

concentration).

MCV (mean corpuscular volume)


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The MCV is calculated from the red blood cell count and the hematocrit

and measures the average size of RBC. It indicates the average

volumeof the erythrocytes in femtoliters (fl = 10^-6 cubic mm). Cell

volume is considered to be microcytic (smaller than normal),

normocytic (normal), or macrocytic (larger than normal). It is

important to interpret the value for MCV along with an inspection of

the peripheral blood smear since the MCV is only a meanvolume. It is

possible to have a wide variation in cell size and still have a normal

MCV. When RBC shape is abnormal, such as in sickle cell anemia, the

MCV is of doubtful value because the hematocrit is not reliable.

MCH (mean corpuscular hemoglobin)

The MCH is calculated from the hemoglobin and the red blood cell

count. It indicates the average weightof hemoglobin in the

erythrocyte in picograms (10^-12/g). It should always correlate with

the MCV and the MCHC. The MCH is directly proportional to the size of

the erythrocyte and the concentration of hemoglobin in the cell. Low

MCH values are found in microcytic anemia and in normocytic,

hypochromic red blood cells. High MCH values are found in macrocytic

anemia and may occur in spherocytosis.

MCHC (Mean corpuscular hemoglobin concentration)

The MCHC is calculated from the hemoblobin and hematocrit. Itindicates the average concentrationof hemoglobin in the erythrocytes

in percentage. A low MCHC indicates hypochromia, seen in iron

deficiency anemia and thasselemia. A high MCHC indicates

hyperchromia, seen in burn patients. The MCHC should never be


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above 38%. A result greater than 38% is usually due to incorrect

calculation or to abnormal agglutination of the patients red blood cells

(such as cold agglutinins) which causes a falsely decreased red blood

cell count. Conversely, the MCHC should never be below 22%. A

result less than 22% may be due to a lipemic specimen or to abnormal

hemoglobin (such as C or S) which causes an invalid hemoglobin

result.

Platelets

Platelets, or thrombocytes, originate from megakaryocytes

cytoplasm in the bone marrow. As the megakaryocyte matures, thecytoplasm increases in amount and becomes more granular. The

granules form small clusters and the cytoplasm breaks into individual

platelets which are released into the peripheral circulation. One

megakaryocyte can produce between 2000 and 4000 platelets. As can

be seen by the formation of the platelets, they have no nucleus. When

there is damage to the endothelium, platelets form thrombi to

decrease the bleeding.In the peripheral blood, the platelet lives 9 12 days.

Approximately 2/3 of the platelets are in the blood, while the

remaining 1/3 forms the platelet pool in the spleen. The platelets in

the spleen and blood are interchangeable.

The role of the platelet is for the purpose of hemostasis, or the

formation of blood clots to decrease bleeding. A decrease in platelets

indicates a high risk for bleeding. When the platelet count is increased,there is a high risk for thrombosis, which can lead to a stroke, heart

attack, or pulmonary emboli.

Normal Values


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(may very slightly according to laboratory method and/or source of

information)

White blood cell count:

Adult 4,500 10,000 cells/microliter

Newborn 9,500-35,000 cells/microliter

One year 6,000 17,000 cells/microliter.

The count continues to drop until it reaches adult levels by age 21.

Red blood cell count:

Adult females 4.2-5.4 x 10^6 cells/microliter

Adult males 4.7-6.1 x 10^6 cells/microliter

Newborn 4.0-5.9 x 10^6 cells/microliter

One year 3.7-4.9 x 10^6 cells/microliter

Children, adolescents, and adults over age 50 may have a slightly

lower RBC count.

Hemoglobin:

Adult females 14-18 grams/deciliter (g/dl)

Adult males 13 18 g/dl

Newborn 17-22 g/dl

One month 11-15 g/dl

One year 11 13 g/dl

Ten years 12 15 g/dl

Hematocrit:

Adult females 38-46%

Adult males 42-54%

Newborn 55-68%


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One year 29-41%

After age 50 there may be a slight decrease in hematocrit.

MCV

Adults 80 100 fl

Newborn 95-115 fl

Two months 74-96 fl

One year 70-84 fl

Ten years 75 87 fl

MCH

Adults 26-34 pg

Newborn 31-37 pg

Two months 25-35 pg

Ten years 25 33 pg

MCHC

Adults 31 37 %

Newborn 31-37 %

Two months 29-37 %

Ten years 31-37 %

The Differential

The differential white blood cell count is performed to determinethe relative number of each type of white blood cell present in the

peripheral blood. They are ordered to determine the presence of a

specific infection, such as viral, bacterial, or parasitic, as well as


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detection of allergic and drug reactions. Red and white blood cells and

platelets are examined for morphological changes.

Normal White Blood Cell Types

Neutrophils These are the largest number of cells in the

granulocytic series. They are the cell most commonly increased in

bacterial infections. The mature form of neutrophil is the

segmented neutrophil. In normal blood there may be some of the

slightly immature form of neutrophil called the band neutrophil.

These bands are often increased when the neutrophil percentage

is high because the hematopoeitic organs release the cells more

rapidly than normal and these younger forms end up in the

peripheral circulation. The main function of the neutrophil is to

ingest and kill invading organisms.

Eosinophil The eosinophil is also in the granulocytic series. They

are primarily tissue cells, and their half-life in blood is only about 8

hours. They usually localize in the skin, nasal membranes, lungs,

and gastrointestinal tract, and they may go back and forth from the

blood to the tissues. Eosinophils can phagocytize foreign material,

and they act as anti-inflammatory cells. They contain histaminase

which can inactivate the histamine from the mast (basophilic) cells.

They may be involved in defense against helminth parasites by

moving to the site of the parasitic infection. The cells then attach

to the surface of the parasites and release hydrolytic enzymes from

their granules. These enzymes damage the larval wall of the

parasites.

Basophils These cells are also part of the granulocytic series of

leukocytes. The basophil shows phagocytic activity. Its granules

contain serotonin, peroxidase, a vasoconstrictive histamine

compound, and heparin. They promote platelet aggregation and


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adhesion. Basophils are involved in immediate hypersensitivity

reactions. If the contents of their granules are released rapidly to

the surrounding area, an anaphylactic shock reaction may occur

which may be severe, such as hyperimmune responses to toxins

and wasp or bee stings. This reaction can result in vasoconstriction

and bronchioconstriction.

Lymphocytes These cells are the next largest number of white

blood cells in the peripheral blood. Their absolute number is often

increased in viral infections. The lymphocytes are vital to the

immune system. Their main function is to produce circulating

antibodies. They also have an important role to play in cellular

immunity.

Monocytes Monocytes, after they have entered tissues, are called

macrophages. Both of these cells are attracted to dead or dying

cells, and they both appear at inflammatory sites. These cells are

also phagocytic, ingesting microorganisms and tumor cells. They

help remove old red blood cells and wound debris as well as plasma

proteins and plasma lipids, and they have a role to play in iron

metabolism. They also release lysosomal enzymes into the

surrounding areas to help decompose tissue and aid the

inflammatory response.

Cellular Morphology on the Differential

Leukocytes Toxic granulation These are cytoplasmic granules in the

neutrophil that appear in infection, drug poisoning, and burns.

Dohle bodies Single or multiple areas in the cytoplasm of the

neutrophil are called Dohle bodies. They consist of rough


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endoplasmic reticulum containing RNA, and they often appear in

infections, poisoning, burns, and after chemotherapy.

Hypersegmented neutrophils Neutrophils with 6 or more

segments in their nucleus represent an abnormality in the

maturation of the cell. Most neutrophils contain 2-4 lobes, with

some having 5 lobes. When there is an increase of the percentage

of 4-5 lobed neutrophils, it will be reported. This is often the case

in pernicious anemia, folic acid deficieny, and chronic infections.

Vacuolated neutrophil When the cytoplasm degenerates and

begins to acquire holes, or as the result of phagocytosis, the

neutrophils appear to be filled with vacuoles, or vacuolated.

These cells often appear in conjunction with septicemia and severe

infection.

Smudge cells These cells are the degenerating nuclei of ruptured

leukocytes.

Enlarged platelets Platelets that are 4 7 microns in diameter

are associated with either increased platelet counts

(thrombocytosis) or decreased platelet counts (thrombocytopenia).

Giant platelets Platelets that are 7-8 microns in diameter can be

seen in myeloproliferative disorders.

Nucleated red blood cells In a normal adult peripheral blood

smear there will be no nucleated red blood cells. When the RBCs

are released from the bone marrow prematurely, possibly as a

result of increased production of red cells due to a need such as

blood loss, they will still contain their nuclei. There may benucleated red blood cells in newborns and this may not be

considered abnormal, depending on the rest of the blood picture.


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Microcytic red blood cells Erythrocytes that are smaller than

normal are found in some anemias, including iron deficiency and

hemolytic anemia.

Macrocytic red blood cells These erythrocytes are larger than

normal and may be seen in liver disease and some anemias, such

as vitamin B12 and folic acid deficiency.

Anisocytosis This describes a situation in which the red blood

cells are various sizes.

Polychromatophilia Polychromatic red blood cells are younger

and slightly larger than normal red cells.

Spherocytes These cells may be present in hemolytic anemia,

hemolytic disease of the newborn, and hereditary spherocytosis.

Target cells These red blood cells have the appearance of a

target. This is associated with abnormal hemoglobin, liver disease,

and sickle cell anemia.

Poikilocytosis This term refers to a variation in shape of the red

blood cells.

Ovalocytes These red blood cells are oval shaped and may be

present in a variety of anemias

Elliptocytes These red blood cells are similar to ovalocytes but

have a more elliptoid, or cigar-shaped, appearance. They may also

be present in various anemias.

Teardrop red blood cells As their name indicates, these cells are

shaped like teardrops, with a pointed end. They may be found in

pernicious anemia, thalassemia, and other anemias.

Crenated red blood cells These cells are also known as burr

cells and have small projections on their outer edges, somewhat

like a burr. Crenation is sometimes an artifact due to drying of the


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blood smear on the slide, but the burr shape may indicate

abnormal conditions such as uremia or acute blood loss.

Schistocytes These are red blood cell fragments. They occur in

hemolytic anemia, uremia, severe burns, and other conditions.

Sickle cells Red blood cells shaped like a sickle or a crescent are

due to the hemoglobin S within the cells. They are associated with

sickle cell anemia, Hemoglobin SC disease, and a form of

thalassemia.

Basophilic stippling Basophilic stippling appears as purple-

staining granules in the red blood cells. The granules are clumps

of ribosomes. This is found in lead poisoning, alcoholism, and

some anemias.

Howell-Jolly bodies These are round nuclear fragments in the red

blood cells. They may appear in anemia and after splenectomy.

Rouleaux formation This is a situation in which erythrocytes are

arranged in stacks, similar to a roll of coins. It may be an artifact

caused by the handling of the blood, or it may be due to a high

concentration of abnormal globulins or fibrinogen. Rouleaux is

found in multiple myeloma and macroglobulinemia.

Agglutination This is clumping of the red blood cells. It is found

in patients who have a cold agglutinin or autoimmune hemolytic

anemia.

Cerebrospinal Fluid (CSF)

A few red blood cells are often found in CSF due to

contamination of the fluid by blood vessels during the lumbar

puncture. The CSF also normally contains a few lymphocytes and

monocytes (white blood cells), the origin of which is uncertain. If a

small number of neutrophils (white blood cells) are present, their


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significance depends on the clinical situation and the results of other

laboratory tests.

Urine Microscopic Examination

Cells in urine vary greatly. Normal urine may contain a few

white blood cells, bacteria, or squamous epithelial cells. (The bacteria

are generally due to urethral contamination.) Red blood cells may be

present in normal urine from females during their menses. Abnormal

cells may include transitional or renal epithelial cells, bacteria (more

than a few), yeast, trichomonas parasite, and an increase in whiteblood cells. Crystals may also be present. They may or may not be

significant, depending on the type of crystal identified.

Hematuria, or blood in urine, is also indicative of UTI,

inflammation, or injury to the urinary system. Also, hematuria is also

indicative of cancers of the bladder, kidney, and prostate.

Pleural and Pericardial Fluid

Total white blood cell and red blood cell counts are of limited

diagnostic value in

pleural and pericardial fluids. However, red blood cell counts higher

than 10,000 per microliter are suggestive of malignancy, trauma, or

pulmonary infarction. Mesothelial cells form the lining of pleural and

pericardial cavities. It is sometimes difficult to distinguish these cells

from malignant cells. During inflammatory processes, mesothelial cells

proliferate and often go into serous fluid.

Summary


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After studying the content of this module, nurses should gain a

better understanding of the complete blood count. They should be

able to evaluate patient situations more quickly, and they should be

able to accurately interpret laboratory descriptions. The bottom line of

the medical profession is healing, and health care professionals cannot

give medical advice or medication without a thorough understanding of

the patients condition. Laboratory tests hold a key to diagnosis and

management of illness. The more information acquired from the

complete blood count and other fluid cell counts, the faster the

diagnosis and treatment. This, in turn, results in improved health care

for the patient.

References

1. Brown, Barbara A. (1993), Hematology, Principles, and

Procedures, 40 82.2.

Miale, John B. (1982), Laboratory Medicine Hematology, 350 357, 379 380.

3.

Tilzer, Lowell L. (1990), Laboratory Test Handbook, 475 478.4. Kjeldsberg, Carl; Knight, Joseph (1986), Body Fluids, 32-42.

5. Sandhaus, Linda M. and Meyer, P. How useful are CBC andReticulocytes to Reports to Clinicians? American Journal of Clinical

Pathology; 2002: 1185(2)6. Nabili, S and Shiel, W.C., Complete Blood Count (CBC)

Accessed on 3/14/10 atwww.medicinenet.com/complete_blood_count/article.htm

7. Dugdale, C. and Chen, YiBen., RBC Updated 3/2/2009.Accessed 3/14/10 on

www.nlm.nih.gov/medlineplus/ency/article/003644.htm8. Campbell, Niel. Biology (8thed) 2008 London: Pearson Edu

9. Complete Blood Count American Association for ClinicalChemistry. 2001- 2010. Last reviewed 3/2/1008. Accessed on 3/14/10at www.labtestsonline.org/understanding/analytes/cbc/test.html

10. Blood in Urine WebMd 2010. accessed 3/17/10 atwww.emedicinehealth.com/blood_in_the_urine/article_em.html

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CBC Basics