Blood Cell Tests

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The blood cell tests presented in this chapter focus on cell number, size, or structure. Tests are presented by individual cell type and include diagnoses related to variations from normal.

Normal ranges of blood cell tests depend on a variety of factors including the age of the individual being tested and the individual laboratory standards where the tests are run. There are a variety of factors that may cause an abnormal test result. These factors are listed with the description of each test.

Complete Blood Count (CBC)

The complete blood count (CBC) is a laboratory test that identifies the number of red and white blood cells per cubic millimeter (mm3) of blood. It is one of the most routinely performed blood tests and provides valuable information about the patient's state of health. The CBC measures and evaluates the cellular component of blood.

The tests included in the complete blood count are white blood cell tests, which include the white blood cell count and the differential white cell count; red blood cell tests, which include the red blood cell count, hematocrit, and hemoglobin count; red blood cell indices, which include the mean corpuscular volume, the mean corpuscular hemoglobin, and the mean corpuscular hemoglobin concentration; and the thrombocyte test, or platelet count. Figure 1-2 is a sample complete blood count report.

PATIENT NAME: Holly, Berry

HEMATOLOGY 1

NORMAL RANGE

RESULTS

Hemoglobin

12-16 g/dl

12.5

Hematocrit

37-47%

36.4

Erythrocytes

4.2-5.4

4.22

Leukocytes

5000-10000/mm3

7800/mm3

Neutrophils

55-70%

85% (H)*

Monocytes

2-8%

4%

Lymphocytes

20-40%

30%

Basophils

0.5-1%

0.7%

Eosinophils

1-4%

2%

Platelet Count

140,000-400,000

500,000 (H)*

MPV

2-4 m/diameter

1.3 m/diameter (L)*

ESR

0-20 mm/hr

10 mm/hr

indicates abnormal: H

= higher than normal and L =

lower than normal.

Figure 1-2. Complete blood count report

White Blood Cell Tests

The white blood cell count and the differential white blood cell count identify the number and type of white blood cells present in the blood. Both tests provide useful diagnostic information.

White Blood Cell Count; Leukocyte Count (WBC)

The white blood cell count identifies the number of white blood cells in a specified volume of blood. The white cell count is then expressed as so many thousand white blood cells per cubic millimeter (/mm3). Cell counting is usually accomplished by an automated cell counter, but can be done using a microscope with a special counting chamber.

Normal Range

Adults and Children 5000-10,000/mm3

Children 2 years or younger 6200-17,000/ mm3 Newborns 9000-30,000/mm3

Variations from Normal. An increase in the overall number of white blood cells is called leukocytosis. This is a very general term and can be the result of a wide variety of conditions such as infection, hemorrhage, trauma, malignancy, general hematologic problems, and leukemia. A decrease in the number of white blood cells is called leukopenia, and can occur for reasons that include viral infections, bone marrow disorders, spleen disorders, immune problems, AIDS, and nutritional deficiencies.

Interfering Circumstances. The white cell count is affected by the time of day (lower levels in the morning and a late afternoon peak), age, and gender. Smoking can cause up to a 30% increase in total white blood cells.

Differential White Blood Cell Count; Differential Leukocyte Count (diff)

The differential white blood cell count is used to identify the percentage of each type of white cell relative to the total number of leukocytes. The five types of leukocytes are neutrophils, eosinophils, basophils, monocytes, and lymphocytes. Each leukocyte has a unique function. Table 1-1 identifies each type of white cell and its function.

Since each of the white cells is unique, normal range and clinical implications of the increase or decrease in each type are presented individually.

Neutrophils

Neutrophils are the most numerous of the white cells and appear to be the body's first defense against bacterial infection and severe stress. During an

Table 1-1. White Blood Cell Identification and Function

Cell

Function

Neutrophil Combats bacterial infection (increase during stress)

Eosinophil Prevents excessive spread of inflammation (responds to allergic disorders and parasitic infections)

Basophil Responsible for allergy symptoms

Monocyte Phagocytizes bacteria, viral material, and cellular debris

Lymphocyte Combats acute viral and chronic bacterial infections; important role in the immune system acute bacterial infection, neutrophils function as phagocytes. Neutrophils remain in the blood stream for approximately 7-10 hours.

Neutrophils are also known as segmented neutrophils (segs) or polymorphonuclear leukocytes (PMNs, polys). The names given to the neutrophils depend on the maturity of the cells and the appearance of the nucleus of the cells. Mature neutrophils are identified by their characteristic segmented or lobed nucleus and are called segs, or segmented neutrophils. Immature neutrophils are called bands or stabs because the nucleus is not segmented.

Normal Range (Adult)

Neutrophils 55-70% of all white cells

Variations from Normal. An increase in the number of circulating neutrophils is called neutrophilia and can be caused by various bacterial infections; inflammatory diseases such as rheumatic fever, rheumatoid arthritis, stress, tissue death or damage; and granulocytic leukemia. When reporting an increase in neutrophils, the terms "shift to the left" or "shift to the right" may be used. A shift to the left simply means that the increase in neutrophils is due to an increase in the number of immature neutrophils. A shift to the right, although rarely used, may indicate that abnormal or mature neutrophils predominate.

A decrease in the number of circulating neutrophils is called neutropenia, and can be caused by viral diseases and infections such as measles, mumps, rubella, hepatitis, and influenza. Bone marrow injury and anorexia nervosa can exhibit neutropenia.

Interfering Circumstances. Various treatments, such as radiation therapy and chemotherapy, carry the risk of decreasing neutrophils. Antibiotics, psychotropic medications, and some antidepressants can also play a role in neutropenia.

Lymphocytes (Lymphs)

Lymphocytes (lymphs) are an important part of the immune system and play an active role in combating acute viral and chronic bacterial infections. There are two types of lymphocytes, T cells and B cells. The differential count does not identify or enumerate the number of T and B cells.

Normal Range (Adult)

Lymphocytes 20-40% of all white cells

Variations from Normal. An increase in the number of lymphocytes is called lymphocytosis and is seen in a variety of diseases. Viral diseases such as rubella, measles, mumps, viral respiratory infections, atypical pneumonia, infectious hepatitis, and infectious mononucleosis exhibit lymphocytosis. Bacterial infections such as syphilis and pertussis can also cause lymphocytosis. Malignant causes of lymphocytosis are lymphocytic leukemia and lymphoma.

A decrease in lymphocytes is called lymphocytopenia and is seen primarily when the immune system is suppressed as in diseases such as AIDS and systemic lupus erythematosus.

Monocytes (Monos)

Monocytes (monos), although small in number, perform an important defense function in the body. These large cells are phagocytes and respond to bacteria in the same manner as neutrophils. Monocytes remain in circulation longer than neutrophils and phagocytize bacterial and cellular debris. Phagocytosis is the process of engulfing and destroying microorganisms and cellular debris. Monocytes also act as phagocytes in some chronic inflammatory diseases such as arthritis.

Normal Range

Monocytes 2-8% of all white cells

Variations from Normal. An increase in the number of monocytes is called monocytosis and is seen during infections such as tuberculosis and bacterial endocarditis. Diseases such as chronic ulcerative colitis, malaria, rheumatoid arthritis, and hemolytic anemia can exhibit an increase in the monocyte count. A decreased monocyte count is not usually identified with any specific disease processes.

Eosinophils and Basophils (Eosinos, Basos)

Eosinophils (eosinos) are minimally phagocytic, but play a role in the antigen-antibody response, in allergic reactions, in combating parasitic infections, and in the dissolution of blood clots. The main function of eosinophils seems to be to prevent the excessive spread of inflammation. Basophils (basos) play an important role in allergic reactions by releasing the histamine that is responsible for allergy symptoms.

Normal Range

Eosinophils 1-4% of all white cells Basophils 0.5-1% of all white cells

Variations from Normal. An increase in eosinophils is called eosinophilia and is associated with allergy attacks, asthma, hay fever, and parasitic infections. Certain skin diseases, tuberculosis, Hodgkin's disease, and granulocytic leukemia result in an increase in eosinophils. A decrease in eosinophils is called eosinopenia and is associated with an increase in adrenal steroid production and acute bacterial or viral inflammation.

An increase in basophils is called basophilia, and is seen in myeloproliferative diseases such as polycythemia vera and chronic granulocytic leukemia. Chicken pox, small pox, chronic sinusitis, and ulcerative colitis may also be present with basophilia. Because the normal basophil count is small to begin with, a decrease in number may not be detected. However, prolonged steroid therapy, hormone imbalance, thyrotoxicosis, and severe allergic reactions often result in a basophil decrease.

Interfering Circumstances. As with other white blood cell counts, age, stress, time of day, and steroid therapy can interfere with eosinophil and basophil counts.

Red Blood Cell Tests

One of the major functions of erythrocytes is to carry oxygen to all parts of the body. In order to do this efficiently, there must be an adequate number of red blood cells and the red blood cells must contain an adequate supply of functioning hemoglobin. Erythrocyte tests include the red blood cell count, hematocrit, and hemoglobin. These tests are closely related and provide different ways to measure the adequacy of red blood cell production and function. Other common red blood cell tests include red blood cell indices and the erythrocyte sedimentation rate.

Red Blood Cell Count; Erythrocyte Count (RBC)

The red blood cell count identifies the number of red blood cells found in a cubic millimeter of blood (mm3). The count is usually accomplished by an electronic or automated counting device.

Normal Range

Men 4.7-6.1 million/mm3

Women 4.2-5.4 million/mm3

Infants and Children 3.8-5.5 million/mm3 Newborns 4.8-7.1 million/mm3

Variations from Normal. A decrease in the number or function of red blood cells is called anemia. Factors that can cause anemia are decreased red blood cell production, increased red blood cell destruction, and blood loss. Certain diseases can also cause a decrease in red blood cells. Some of these diseases include Hodgkin's disease, leukemia, rheumatic fever, and diseases that affect the bone marrow where red blood cells are produced.

An increase in the number of red blood cells is called erythrocytosis, a slight increase, or erythremia, an excessive increase. Many factors can contribute to this increase, such as an overproduction of red blood cells or a decrease in the amount of blood plasma. Conditions such as dehydration, severe diarrhea, acute poisoning, and chronic lung disease can also cause an increase in the red blood cell count.

Interfering Circumstances. The results of the red blood cell count can be altered by several nondisease situations. These would include the posture or position of the patient when the blood was drawn, exercise, age, altitude, pregnancy, and various legal and illegal drugs.

Hematocrit (Hct); Packed Cell Volume (PCV)

The purpose of the hematocrit or packed cell volume (PCV) test is to determine the percentage of red blood cells in whole blood. The hematocrit is reported as a percentage because it is the proportion of red blood cells compared to the amount of plasma in whole blood.

The term "hematocrit" literally means to separate blood. A sample of blood is placed in a tube that contains an anticoagulant, which prevents clotting. The sample is mixed, and three distinct layers will separate out. Figure 1-3 shows these three layers.

The bottom layer represents the hematocrit value and is composed of red blood cells, approximately 45% of the total blood volume, with variations allowed for men and women. The middle layer is a thin, whitish layer called the buffy coat, approximately 1% of the blood volume, which is made

Plasma

Buffy Coat

Red Blood Cells

Plasma

Buffy Coat

WBC Platelets

Red Blood Cells

Figure 1-3. The three layers of normal blood after settling in a tube.

up of white blood cells and platelets. The upper layer is the liquid plasma, which comprises the remainder of the total blood volume.

Normal Range

Children 30-42% Newborns 44-64%

Variations from Normal. Since the hematocrit is the percentage of red blood cells in whole blood, a decrease in hematocrit values is an indication of some type of anemia. Therefore, anything that causes a decrease in the number of red blood cells will result in a decrease in the hematocrit. Blood loss, conditions where there is increased destruction of red blood cells, leukemia, and diseases that interfere with red blood cell production will exhibit a low hematocrit. It must also be noted that overhydration, or an increase in plasma volume for any reason, can result in a relative decreased hematocrit value.

An apparent increase in the hematocrit must be closely analyzed. Since the hematocrit is reported as a percentage of red blood cells to blood volume, any decrease in the volume of plasma would result in a mathematical increase in the hematocrit. Therefore, if the patient has lost blood plasma, the blood will be very concentrated and the hematocrit will be increased. When an increase in hematocrit is related to the increase in the actual number of red blood cells, erythrocytosis or polycythemia is the result.

Interfering Circumstances. Factors that can influence hematocrit results include age, pregnancy, gender, and living in high altitudes.

Hemoglobin (Hgb)

Hemoglobin is a protein-iron complex that is the main constituent of red blood cells. In fact, red blood cells contain approximately 90% hemoglobin. The primary functions of hemoglobin are to transport oxygen from the lungs to the cells and to carry carbon dioxide from the cells to the lungs to be expelled. The hemoglobin test is used to indirectly evaluate the oxygen-carrying capacity of the red blood cells. The hemoglobin count is also used to diagnose, evaluate, or assess the treatment of various types of anemia.

Men Women

A normal red blood cell count does not automatically translate into a normal hemoglobin value. Abnormal production of any portion of hemoglobin could result in decreased levels of hemoglobin per red blood cells. Once a sample of blood is taken, the hemoglobin level is determined by automated electronic equipment. Generally, the hemoglobin value is approximately one-third of the hematocrit value. Therefore, a person with a 45% hematocrit would be expected to have approximately 15 grams of hemoglobin per deciliter of blood (15 g/dl).

Normal Range

Men 14-18 g/dl

Women 12-16 g/dl (in pregnancy: >11 g/dl) Children 11-16 g/dl Newborns 14-24 g/dl

Variations from Normal. Hemoglobin levels can exhibit temporary variations immediately after blood transfusions, hemorrhages, and burns. A decrease in the hemoglobin level can be found in various anemias. Other diseases and factors that result in a hemoglobin decrease include hyperthyroidism, cirrhosis of the liver, transfusions of incompatible blood, Hodgkin's disease, lymphoma, and reactions to various chemicals and drugs. Since iron is necessary for the production of hemoglobin, a decreased hemoglobin level may signal the need for blood iron tests. These tests are described in Chapter 3, Blood Chemistry Tests.

An increase in hemoglobin levels is found in any situation that results in an increased number of healthy red blood cells. Diseases associated with increased hemoglobin values are chronic obstructive pulmonary disease and congestive heart failure.

Interfering Circumstances. Factors that can affect hemoglobin results include pregnancy, altitude, age, gender, and excessive fluid intake. Various medications may cause an increase or decrease in hemoglobin levels.

Red Blood Cell Indices

The red blood cell indices are used to determine the size of the erythrocyte and the hemoglobin content of the red blood cells, and to identify specific types of anemia. The indices are not individual blood cell tests, but are the result of applying mathematical formulas to the hemoglobin value, hematocrit value, and red blood cell count. Each index has its own formula that is automatically computed as a part of the complete blood count.

Red blood cell indices include the mean corpuscular volume, which describes the average volume (size) of an individual red blood cell; the mean corpuscular hemoglobin, the average weight of the hemoglobin in an average red blood cell; and the mean corpuscular hemoglobin concentration, which is the average concentration or percentage of hemoglobin within each red blood cell.

Mean Corpuscular Volume (MCV)

The mean corpuscular volume describes the average size of an individual red blood cell in cubic microns (|J.m3), and is calculated by multiplying the hematocrit percentage by 10, and then dividing that result by the red blood cell count. The size of red blood cells can have clinical significance in various types of anemia.

Normal Range

Adults and Children 80-95 ^m3 Newborns 96-108 |im3

Variations from Normal. When there is a decrease in the mean corpuscular volume, the erythrocytes are microcytic, or smaller than normal. Microcytic red blood cells are seen in iron deficiency anemia, lead poisoning, and thalassemia.

An increase in the mean corpuscular volume indicates that the red blood cells are macrocytic, or larger than normal. Pernicious anemia is associated with macrocytic red blood cells.

When the mean corpuscular volume is within normal range, the red blood cells are normocytic, or of normal size. Aplastic, hemolytic, and temporary blood loss anemia are associated with red blood cells that are normal in size.

Mean Corpuscular Hemoglobin (MCH)

The mean corpuscular hemoglobin is the average weight of hemoglobin in an average red blood cell. This weight is calculated by multiplying the hemoglobin count by 10 and then dividing by the red blood cell count. The result is reported in picograms (pg). The mean corpuscular hemoglobin is adequate for diagnosing severely anemic patients, but is a nonspecific result.

Normal Range

Adults and Children 27-31 pg Newborns 32-38 pg

Variations from Normal. An increase in the mean corpuscular hemoglobin is seen in macrocytic anemia, while a decrease is associated with microcytic anemia.

Mean Corpuscular Hemoglobin Concentration (MCHC)

The mean corpuscular hemoglobin concentration measures the average concentration or percentage of hemoglobin within each red blood cell. The MCHC is calculated by dividing the hemoglobin value by the hematocrit value, and multiplying the result by 100. The mean corpuscular hemoglobin concentration is most valuable for classifying anemias.

Normal Range

Adults and Children 32-36% Newborns 32-33%

Variations from Normal. A decrease in the mean corpuscular hemoglobin concentration indicates that the red blood cells contain less hemoglobin than normal and is classified as hypochromic anemia, which means the red blood cells lack color. Iron deficiency anemia is the most common type of hypochromic anemia.

An increase in the mean corpuscular hemoglobin concentration usually indicates spherocytosis. Spherocytosis is defined as an increase in the number of abnormal, spheric, red blood cells called spherocytes. Sphero-cytes have a smaller amount of membrane and a full complement of hemoglobin so the mean corpuscular hemoglobin concentration is elevated. Table 1-2 lists the classifications of anemia based on the red blood cell indices values.

Table 1-2. Anemias and Associated Red Blood Cell Indices

Red Blood

Iron Deficiency

Blood Loss

Pernicious

Cell Index

Anemia

Anemia

Anemia

MCV

Decreased

Normal

Increased

MCH

Decreased

Normal

Variable

MCHC

Decreased

Normal

Variable

RBC size

Microcytic

Normocytic

Macrocytic

RBC color

Hypochromic

Normochromic

Not applicable

Erythrocyte Sedimentation Rate (ESR, Sed Rate)

The erythrocyte sedimentation rate is the rate at which red blood cells settle out of unclotted blood in an hour. The results are expressed as millimeters per hour (mm/hr). This is a nonspecific test because it does not identify any particular disease. In fact, the ESR can be normal in many disease processes.

The erythrocyte sedimentation rate is useful in determining the progress of inflammatory diseases, rheumatoid arthritis, rheumatic fever, and acute myocardial infarction. The speed at which the red blood cells fall to the bottom of the test tube corresponds to the degree of inflammation.

Normal Range

Women <50 yrs 0-13 mm/hr

Children 0-10 mm/hr

Variations from Normal. An increase in the sed rate is usually due to inflammation or tissue injury. When sed rates are greater than 100 mm/hr, likely causes, except in pregnancy, are infections, malignancies or collagen vascular diseases. A decrease in the sed rate is associated with polycythemia vera, sickle cell anemia, and a deficiency in the plasma protein fibrinogen.

Interfering Circumstances. Many factors can influence the erythrocyte sedimentation rate. Refrigerated blood samples, blood left standing for more than two hours before the test, menstruation, and pregnancy will cause a nonpathological increase in this test. Age and certain drug therapies may also cause variations in test results.

Platelet Count Tests

Platelets, also called thrombocytes, are the smallest cells in the blood. These cells do not have a nucleus, are round or oval, flattened, disk-shaped structures, and are necessary for coagulation. Some texts refer to platelets as fragments of cytoplasm.

Two tests that measure or count the number of platelets are the platelet count, which measures the number of platelets in the blood, and the mean platelet volume (MPV), which provides information about platelet size. Platelet function tests are covered in Chapter 4, Coagulation Studies.

Platelet Count

A platelet count test often follows a decreased platelet count that was estimated from a peripheral blood smear. The platelet count is an important blood test because thrombocytopenia is the most common cause of bleeding diseases. This count is used to evaluate bleeding disorders due to liver disease, thrombocytopenia, and anticoagulant therapy. The test is also ordered for patients who have diseases associated with bone marrow problems, such as leukemia and aplastic anemia. The platelet count is expressed as the number of platelets per cubic millimeter (mm3) of blood.

Normal Range

Platelets 150,000-400,000/mm3

Variations from Normal. An abnormal increase in the number of platelets is called thrombocythemia or thrombocytosis. This increase is seen in diseases such as malignancies, early stages of chronic granulocytic leukemia, polycythemia vera, tuberculosis, chronic inflammatory disease, and chronic blood loss.

A decreased platelet count is known as thrombocytopenia and can result in significant bleeding problems. Diseases that decrease the platelet count include pernicious and aplastic anemias, and idiopathic thrombocytopenic purpura (ITP). A low platelet count is commonly seen in AIDS cases. Exposure to various chemicals and the toxic effects of many drugs can also lead to thrombocytopenia. Individuals who have serious platelet deficits often show signs or symptoms such as petechiae, bleeding from gums, nosebleeds, and gastrointestinal bleeding.

Interfering Circumstances. Platelet counts can show a normal increase at high altitudes, after strenuous exercise, and in the winter. A normal decrease occurs on the first day of an infant's life and before menstruation.

Mean Platelet Volume (MPV)

The mean platelet volume provides information about the relative size of platelets, which is calculated by a cell analyzer and compared to what is observed on a microscope slide. The diameter of the platelet is expressed in micrometers (|im). The MPV is a useful diagnostic tool for thrombocytopenic disorders.

The relative size of platelets varies with platelet production. When the overall platelet count drops, functioning bone marrow produces younger and larger platelets to compensate for the decreased number of platelets. This process results in an increased mean platelet volume. Lack of bone marrow function results in the decreased production of platelets, a diminished platelet size, and a decreased mean platelet volume.

Normal Range

Platelets 2-4 jxm in diameter

Variations from Normal. An increase in the diameter of the platelets occurs in systemic lupus erythematosus, idiopathic thrombocytopenic purpura in remission, various anemias, myeloproliferative disorders, and a variety of chronic disease processes. A decrease in the size of platelets is associated with aplastic anemia, megaloblastic anemia, and hypersplenism.

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  • genoveffa palerma
    What is result of bacterial infection on hemacrit?
    5 years ago

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