The Vascular System

FUNCTIONS

The vascular system is the system of blood vessels that, along with the heart, forms the closed loop through which blood is circulated to all parts of the body. There are two divisions to this system, the pulmonary circulation and the systemic circulation.

The Pulmonary Circulation

The pulmonary circulation carries blood from the right ventricle of the heart to the lungs to remove carbon dioxide and pick up oxygen; the oxygenated blood is then returned to the left atrium of the heart.

The Systemic Circulation

The systemic circulation serves the rest of the body, carrying oxygenated blood and nutrients from the left ventricle of the heart to the body cells and then returning to the right atrium of the heart with blood carrying carbon dioxide and other waste products of metabolism from the cells.

STRUCTURES

The structures of the vascular system are the various blood vessels that, along with the heart, form the closed system through which blood fl ows. Blood vessels are tubelike structures ca-pable of expanding and contracting. According to information from the Arizona Science Cen-ter, the human vascular system has around 250,000 miles of blood vessels, 95% of which are capillaries, which make up what is called the capillary bed. The rest are arteries and veins.

Arteries

Arteries are blood vessels that carry blood away from the heart. They have thick walls because the blood that moves through them is under pressure from the contraction of the ven-tricles. This pressure creates a pulse that can be felt, distinguishing the arteries from the veins.

The smallest branches of arteries that join with the capillaries are called arterioles (ar-te’re-olz). The largest artery in the body is the aorta. It is approximately 1 inch (2.5 cm) in diameter.

Veins

Veins are blood vessels that return blood to the heart. Veins carry blood that is low in oxygen (deoxygenated or oxygen-poor) except for the pulmonary vein, which carries oxygenated blood from the lungs back to the heart. Because systemic venous blood is oxygen-poor, it is much darker and more bluish-red than normal arterial blood.

The walls of veins are thinner than those of arteries because the blood is under less pres-sure than arterial blood. Since the walls are thinner, veins can collapse more easily than ar-teries. Blood is kept moving through veins by skeletal muscle movement, valves that prevent the backfl ow of blood, and pressure changes in the abdominal and thoracic cavities during breathing.

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The smallest veins at the junction of the capillaries are called venules (ven’ulz). The largest veins in the body are the venae cavae (singular, vena cava). The longest veins in the body are the great saphenous (sa-fe’nus) veins in the leg.

Capillaries

Capillaries are microscopic, one-cell-thick vessels that connect the arterioles and venules, forming a bridge between the arterial and venous circulation. Blood in the capillaries is a mixture of both venous and arterial blood. In the systemic circulation, arterial blood delivers oxygen and nutrients to the capillaries. The thin capillary walls allow the ex-change of oxygen for carbon dioxide and nutrients for wastes between the cells and the blood. Carbon dioxide and wastes are carried away in the venous blood. In the pulmonary circulation, carbon dioxide is delivered to the capillaries in the lungs and exchanged for oxygen.

BLOOD VESSEL STRUCTURE

Arteries and veins are composed of three main layers. The thickness of the layers varies with the size and type of blood vessel. Capillaries are composed of a single layer of endothelial cells enclosed in a basement membrane.

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Layers

• Tunica (tu’ni-ka) adventitia (ad’ven-tish’e-a): the outer layer of a blood vessel, some-times called the tunica externa. It is made up of connective tissue and is thicker in arter-ies than in veins.

• Tunica media: the middle layer of a blood vessel. It is made up of smooth muscle tissue and some elastic fi bers. It is much thicker in arteries than in veins.

• Tunica intima (in’ti-ma): the inner layer or lining of a blood vessel, sometimes called the tunica interna. It is made up of a single layer of endothelial cells with an underlying basement membrane, a connective tissue layer, and an elastic internal membrane.

CO2

Venule(small vein) Tissue

fluid

Lymphaticcapillary Arteriole

(small artery)

ErythrocyteLeukocyteBloodcapillary

Bodycells

Valve

O2

The oxygen and carbon dioxide exchange in the tissue capillaries.

Lumen

The internal space of a blood vessel through which the blood fl owsss is called th lumen (lu’men).

Tunica intima(endothelium)

Valve

Elastic tissue

Tunica media(smooth muscle)

Tunica adventitia(connective tissue)

Artery Vein

Arteriole

Blood flow

Venule

Capillaries

Valves

Venous valves are thin membranous leafl ets composed primarily of epithelium similar to that of the semilunar valves of the heart. Most of the venous system fl ows against the pull of gravity. As blood is moved forward by the movement of skeletal muscle, for example, the valves help keep it fl owing toward the heart by allowing blood to fl ow in only one direction.

To heartTo heart

Proximalvalve closes

VeinVein

Distalvalve opens

Proximalvalve opens

Skeletalmusclecontracts

Skeletalmusclerelaxes

Distalvalve closes

A B

A. Contracting skeletal muscle com-presses the vein and drives blood forward, opening the proximal valve, while the distal valve closes to prevent backfl ow of blood. B. When the muscles relaxes again, the distal valve opens and the proximal valve closes until blood moving in the vein forces it open again.

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THE FLOW OF BLOOD

The network of arteries, veins, and capillaries forms the pathway for the fl ow of blood throughout the body; it allows for the delivery of oxygen and nutrients to the body cells and the removal of carbon dioxide and other waste products of metabolism.

PHLEBOTOMY-RELATED VASCULAR ANATOMY

Antecubital Fossa

Antecubital (an’te-ku’bi-tal) means “in front of the elbow.” Fossa means a shallow depres-sion. The antecubital (AC) fossa is the shallow depression in the arm that is anterior to (in front of) and below the bend of the elbow. It is the fi rst-choice location for venipuncture because several major arm veins lie close to the surface in this area, making them relatively easy to locate and penetrate with a needle. These major superfi cial veins are referred to as antecubital veins. The anatomical arrangement of antecubital veins varies slightly from per-son to person; however, two basic vein arrangements, referred to as the H- and M-shaped patterns, are seen most often.

H-Shaped Antecubital Veins The H-shaped venous distribution pattern is displayed by approximately 70% of the population and includes the

median cubital vein, cephalic vein, and basilic vein.

Median cubital vein: Located near the center of the antecubital area, it is the preferred vein for venipuncture in the H-shaped pattern. It is typically larger, closer to the surface, better anchored, and more stationary than the others, making it the easiest and least painful to puncture and the least likely to bruise.

• Cephalic vein: Located in the lateral aspect of the antecubital area, it is the second-choice vein for venipuncture inthe H-shaped pattern. It is often harder to palpate than the median cubital but is fairly well anchored and often theonly vein that can be pal-pated (felt) in obese patients.

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Basilic vein: A large vein located on the medial aspect (inner side) of the antecubital area, it is the last-choice vein for venipuncture in either venous distribution pattern. It is generally easy to palpate but is not as well anchored and rolls more easily, increasing the possibility of accidental puncture of the anterior or posterior branch of the medial cutaneous nerve (a major nerve of the arm) or the brachial artery, both of which com-monly underlie this area. Punctures in this area also tend to be more painful.

•

Basilic vein

Ant. mediancutaneous nerve

Post. mediancutaneous nerve

Brachialartery

Cephalicvein

Cephalicvein

Accessorycephalic

veinMedian cubital vein

Medial cubitalnerve

A. H-Pattern B. M-Pattern Dorsal Forearm, Wrist,and Hand Veins

C.

Subclavianvein

Basilic vein

Median vein

Brachial artery

Cephalic vein

Cephalic vein

Accessorycephalic vein

Mediancephalic vein

Basilic vein

Ant. mediancutaneous nervePost. mediancutaneous nerve

MedialcubitalnerveSubclavianvein

Basilic vein

Median basilicveinMedian vein

CephalicveinBasilic vein

Dorsalmetacarpal

veins

M-Shaped Antecubital Veins

The veins that form the M-shaped venous distribution pattern include the cephal-ic vein, median vein, median cephalic vein, median basilic vein, and basilic vein. The veins most commonly used for venipuncture in this distribution pattern are described as follows:

• Median vein (also called the intermediate antebrachial vein): The fi rst choice for venipuncture in the M-shaped pattern because it is well anchored, tends to be less pain-ful to puncture, and is not as close to major nerves or arteries as the others, making it generally the safest one to use.

• Median cephalic vein (also called the intermediate cephalic vein): The second choice for venipuncture in the M-shaped pattern because it is accessible and is for the most part located away from major nerves or arteries, making it generally safe to puncture. It is also less likely to roll and relatively less painful to puncture.

• Median basilic vein (also called the intermediate basilic vein): The last choice for venipuncture in the M-shaped pattern (even though it may appear more accessible) be-cause it is more painful to puncture and, like the basilic vein, is located near the anterior and posterior branches of the medial cutaneous nerve and the brachial artery.

Leg, Ankle, and Foot Veins

Because of the potential for signifi cant medical complications such as phlebitis or thrombo-sis, veins of the leg, ankle, and foot must not be used for venipuncture without permission from the patient’s physician. Puncture of the femoral vein is performed only by physicians or specially trained personnel.

Arteries

Arteries are not used for routine blood collection. Arterial puncture requires special training to perform, is more painful and hazardous to the patient, and is generally limited to the collection of arterial blood gas (ABG) specimens for the evaluation of respiratory function.

The Blood

Blood has been referred to as “the river of life,” as it fl ows throughout the circulatory system delivering nutrients, oxygen, and other substances to the cells and transporting waste prod-ucts away from the cells for elimination.

BLOOD COMPOSITION

Blood is a mixture of fl uid and cells; it is about fi ve times thicker than water, salty to the taste, and slightly alkaline, with a pH of about 7.4 (pH is the degree of acidity or alkalinity on a scale of 1 to 14, with 7 being neutral). In vivo (in the living body), the fl uid portion of the blood is called plasma; the cellular portion is referred to as the formed elements. The average adult weighing 70 kg (approximately 154 pounds) has a blood volume of about 5 liters (5.3 quarts), of which approximately 55% is plasma and 45% is formed elements. Accordingly, approximately one half of a blood specimen will be serum or plasma and the other half will be blood cells.

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PlasmaNormal plasma is a clear, pale-yellow fl uid that is nearly 90% water (H2O) and 10% solutes (dissolved substances). The

composition of the solute includes the following:

• Gases, such as oxygen (O2), carbon dioxide (CO2), and nitrogen (N).

• Minerals such as sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg). Sodi-um helps maintain fl uid balance, pH, and calcium and potassium balance is necessary for normal heart action. Potassium is essential for normal muscle activity and the conduction of nerve impulses. Calcium is needed for proper bone and tooth formation, nerve conduc-tion, and muscle contraction. In addition, calcium is essential to the clotting process.

• Nutrients, which supply energy. Plasma nutrients include carbohydrates, such as glucose, and lipids (fats), such as triglycerides and cholesterol.

• Proteins, such as albumin, which is manufactured by the liver and functions to help regulate osmotic pressure, or the tendency of blood to attract water; antibodies, which combat infection; and fi brinogen, which is also manufactured by the liver and functions in the clotting process.

• Waste products of metabolism such as blood urea nitrogen (BUN), creatinine, and uric acid.

• Other substances such as vitamins, hormones, and drugs.

Formed Elements

Erythrocytes

Erythrocytes (e-rith’ro-sites), or red blood cells (RBCs), are the most numerous cells in the blood, averaging 4.5 to 5 million per cubic millimeter of blood. Their main func-tion is to carry oxygen from the lungs to the cells. They also carry carbon dioxide from the cells back to the lungs to be exhaled.

RBCs are produced in the bone marrow. They are formed with a nucleus, which they lose as they mature and enter the bloodstream. Normally a few reticulocytes (re-tik’u-lo-sits), or “retics” (immature RBCs that still contain remnants of material from their nuclear stage), also enter the bloodstream. Mature RBCs have a life span of approximately 120 days, after which they begin to disintegrate and are removed from the bloodstream by the spleen and liver. They are described as anuclear (having no nuclei), biconcave (indented from both sides) disks approximately 7 to 8 microns in diameter. RBCs have intravascular (within blood vessels) function, which means that they do their job within the bloodstream.

Leukocytes

Leukocytes, or white blood cells (WBCs), contain nuclei. The average adult has from 5,000 to 10,000 WBCs per cubic millimeter of blood. WBCs are formed in the bone marrow and lymphatic tissue. They are said to have extravascular (outside the blood vessels) function because they are able to leave the bloodstream and do their job in the tissues. WBCs may appear in the bloodstream for only 6 to 8 hours but reside in the tissues for days, months, or even years. The life span of WBCs varies with the type.

Platelet

Leukocyte

Erythrocytes

The main function of WBCs is to neutralize or destroy pathogens. Some accomplish this by phagocytosis (fag’o-si-to’sis), a process in which a pathogen or foreign matter is surrounded, engulfed, and destroyed by the WBC. (WBCs also use phagocytosis to remove disintegrated tissue.) Some WBCs produce antibodies that destroy pathogens indirectly or release sub-stances that attack foreign matter.

There are different types of WBCs, each identifi ed by its size, the shape of the nucleus, and whether or not there are granules present in the cytoplasm when the cells in a blood smear are stained with a special blood stain called Wright’s stain. WBCs containing easily visible granules are called granulocytes (gran’u-lo-sites’). WBCs that lack granules or have extremely fi ne granules that are not easily seen are called agranulocytes.

Granulocytes

Granulocytes can be differentiated by the color of their granules when stained with Wright’s stain. There are three types of granulocytes: neutrophils, eosinophils (“eos”), and basophils (“basos”). Neutrophils are normally the most numerous type of WBC in adults. A typical neutrophil is polymorphonuclear, meaning its nucleus has several lobes or segments, and is also called a “poly,” “PMN,” or “seg” for short.

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Agranulocytes

There are two types of agranulocytes: monocytes (“monos”) and lymphocytes (“lymphs”). Lymphocytes are normally the second most numerous type of WBC and the most numerous agranulocyte. Two main types of lymphocytes are T lymphocytes and B lympho-cytes. Monocytes are the largest WBCs.

Thrombocytes

Thrombocytes (throm’bo-sits), better known as platelets, are the smallest of the formed elements. Platelets are actually parts of a large cell called a megakaryocyte (meg’a-kar’e-o-sit’), which is found in the bone marrow. The number of platelets in the blood (platelet count) of the average adult ranges from 150,000 to 400,000 per cubic millimeter. Platelets are essential to coagulation (the blood-clotting process) and are the fi rst cell on the scene when an injury occurs (see “Hemostasis,” below). The life span of a platelet is about 10 days.

BLOOD TYPE

An individual’s blood type (also called blood group) is inherited and is determined by the presence or absence of certain proteins called antigens on the surface of the red blood cells. Some blood-type antigens cause formation of antibodies (also called agglutinins) to the op-posite blood type. Some antibodies to blood-type antigens are preformed in the blood. (A person will not normally have or produce antibodies against his or her own RBC antigens.) If a person receives a blood transfusion of the wrong type, the antibodies may react with the donor RBCs and cause them to agglutinate (a-gloo’tin-ate), or clump together, and lyse (lı¯s)—that is, to hemolize or disintegrate. Such an adverse reaction between donor cells and a recipient, which can be fatal, is called a transfusion reaction. The most commonly used method of blood typing recognizes two blood group systems: the ABO system and the Rh factor system.

ABO Blood Group System

The ABO blood group system recognizes four blood types, A, B, AB, and O, based on the presence or absence of two antigens identifi ed as A and B. An individual who is type A has the A antigen, type B has the B antigen, type AB has both antigens, and type O has neither A nor B. Type O is the most common type, and type AB is the least common.

Unique to the ABO system are preformed antibodies in a person’s blood that are directed against the opposite blood type. Type A blood has an antibody (agglutinin) directed against type B, called anti-B. A person with type B has anti-A, type O has both anti-A and anti-B, and type AB has neither. Table 6-6 shows the antigens and antibodies present in the four ABO blood types.

Individuals with type AB blood were once referred to as universal recipients because they have neither A nor B antibody to the RBC antigens and can theoretically receive any ABO type blood. Similarly, type O individuals were once called universal donors because they have neither A nor B antigen on their RBCs, and in an emergency, their blood can theoretically be given to anyone. However, type O blood does contain plasma antibodies to both A and B antigens, and when given to an A or B type recipient, it can cause a mild transfusion reaction. To avoid reactions, patients are usually given type-specific blood, even in emergencies.

ABO Blood Group System

Blood Type RBC Antigen Plasma Antibodies (Agglutinins)

A A Anti-B

B B Anti-A

AB A and B Neither anti-A nor anti-B

O Neither Anti-A and anti-B

Rh Blood-Group System

The Rh blood-group system is based upon the presence or absence of an RBC antigen called the D antigen, also known as Rh factor. An individual with the D antigen present on red blood cells is said to be positive for the Rh factor, or Rh-positive (Rh�). An individual whose RBCs lack the D antigen is said to be Rh-negative (Rh�). A patient must receive blood with the correct Rh type as well as the correct ABO type. Approximately 85% of the population is Rh�.

Unlike the ABO system, antibodies to the Rh factor (anti-Rh antibodies) are not preformed in the blood of Rh� individuals. However, an Rh� individual who receives Rh� blood can become sensitized. This means that the individual may produce antibodies against the Rh fac-tor. In addition, an Rh� woman who is carrying an Rh� fetus may become sensitized by the RBCs of the fetus, most commonly by leakage of the fetal cells into the mother’s circulation during childbirth. This may lead to the destruction of the RBCs of a subsequent Rh� fetus, because Rh antibodies produced by the mother can cross the placenta into the fetal circula-tion. When this occurs, it is called hemolytic disease of the newborn (HDN).

Compatibility Test/Cross-Match

Other factors in an individual’s blood can cause adverse reactions during a blood transfusion, even with the correct ABO- and Rh-type blood. Consequently, a test to determine if the donor unit of blood and the blood of the patient recipient are compatible (suitable to be mixed to-gether) is performed using patient serum and cells as well as serum and cells from the donor unit. This test is called a compatibility test or cross-match.

BLOOD SPECIMENS

Serum

Blood that has been removed from the body will coagulate or clot within 30 to 60 minutes. The clot consists of the blood cells enmeshed in a fi brin network (see “Hemostasis,” below). The remaining fl uid portion is called serum and can be separated from the clot by centrifu-gation (spinning the clotted blood at very high speed in a machine called a centrifuge). Normal fasting serum is a clear, pale-yellow fl uid. Serum has the same composition as plasma except that it does not contain fi brinogen, because the fi brinogen was used in the formation of the clot. Many laboratory tests, especially chemistry and immunology tests, are performed on serum.

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Plasma

Not all tests can be performed on serum. For example, most coagulation tests cannot be performed on serum because some of the coagulation factors (e.g., fi brinogen) are used up in the process of clot formation. Some chemistry tests, such as ammonia and potas-sium, cannot be performed on serum because clotting releases these substances from the cells. In addition, some chemistry test results are needed stat (immediately) in order to respond to emergency situations; having to wait 30 minutes or more for a specimen to clot before centrifuging it to get serum would be unacceptable. If clotting is prevented, however, coagulation factors and other substances affected by clotting are preserved, and the specimen can be centrifuged immediately. Blood can be prevented from clotting by adding a substance called an anticoagulant. Adding an anticoagulant initially creates a whole-blood specimen. When a whole-blood specimen is centrifuged, it separates into three distinct layers: a bottom layer of red blood cells; a thin, fl uffy-looking, whitish-colored middle layer of WBCs and platelets referred to as the buffy coat; and a top layer of liquid called plasma, which can be separated from the cells and used for testing. Normal fasting plasma is a clear to slightly hazy pale-yellow fl uid visually indistinguishable from serum. The major difference between plasma and se-rum is that plasma contains fi brinogen. Many laboratory tests can be performed on either serum or plasma.

Buffy coat (WBCs and platelets)

Plasma

Red blood cells

Whole Blood

Some tests, including most hematology tests and some chemistry tests such as glycohemoglo-bin, cannot be performed on serum or plasma. These tests must be performed on whole blood (blood in the same form as it is in the bloodstream). This means that the blood specimen must not be allowed to clot or separate. To obtain a whole-blood specimen, it is necessary to add an anticoagulant. In addition, because the components will separate if the specimen is allowed to stand undisturbed, the specimen must be mixed for a minimum of 2 minutes immediately prior to performing the test.

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Hemostasis and Coagulation

Hemostasis (he’mo-sta’sis), which means the arrest or stoppage of bleeding, is the body re-sponse that stops the loss of blood after injury without affecting the fl ow of blood within the rest of the vascular system. (The opposite of hemostasis is hemorrhage.) The hemostatic pro-cess requires the coordinated interaction of endothelial cells lining the blood vessels, plate-lets, other blood cells, plasma proteins, and the coagulation (clotting) process.

Ongoing daily repair of vessels keeps the hemostatic process active at a low level all the time as cells die and are replaced. When a blood vessel is injured, it immediately begins to repair the damage. This involves four interrelated responses: (a) vasoconstriction; (b) formation of a primary platelet plug in the injured area; (c) progression, if needed, to a stable blood clot called the secondary hemostatic plug; and (d) fibrinolysis, the dissolving of the clot after the site has healed .

THE ROLE OF THROMBIN

The enzyme thrombin plays the major role in coagulation. It is generated at the injured site from prothrombin (factor II), its precursor form present in the blood. The primary role of thrombin is to convert fi brinogen to soluble fi brin. Thrombin also amplifi es (intensi-fi es) coagulation, supports platelet plug formation, activates factor XIII to cross-link fi brin, and controls its own formation and the coagulation process by activating protein C, a substance that helps stop thrombin formation. Once healing has occurred, thrombin initi-ates the breakdown of the fi brin-reinforced clot by its role in the production of an enzyme that causes clot lysis. Thrombin is also thought to play a role in infl ammation and wound healing.

Activated clotting factors

produce prothrombin

activator (PTA)

Injured vessel

Prothrombin

Blood clot

Fibrinogen

Fibrin fibers

Trapped red blood cells (RBCs)

Thrombin

Ca++

FIBRINOLYSIS

Fibrinolysis (fi ’brin-ol’i-sis), the process by which fi brin is dissolved, is an ongoing process responsible for two important activities: (a) it dissolves clots that form within intact vessels (thrombi), thus reopening the vessels, and (b) it removes hemostatic clots from the tissue as healing occurs. The process is possible because activation of the clotting process also activates factors like XIIa and promotes release of plasminogen activators from vessel lining cells and white blood cells. These substances convert plasminogen to plasmin. Plasmin is the enzyme that breaks down fi brin into smaller fragments called fi brin degradation products (fibrin split products and D-dimers), which are then removed by phagocytic cells.

Hematologic TestingCommon hematology tests include complete blood count (CBC), erythrocyte sedimentation rate (ESR, or sed rate), and coagulation tests. Clinical Laboratory Improvement Amendment (CLIA) regulations limit the types of hematology testing medical assistants can per-form. The list of hematology tests medical assistants can perform, updated regularly by the Centers for Medicare and Medicaid Services (CMS), includes the following:

• ESR (not automated)• Hematocrit (all spun microhematocrit procedures)• Hemoglobin (selected methods)• Prothrombin time (selected methods)

Complete Blood CountMore than just for hematology, the CBC is the most fre-quently ordered test in the entire laboratory. It consists of a number of parameters, including the following:

• WBC count and differential• RBC count• Hemoglobin• Hematocrit• Mean cell volume (MCV)• Mean corpuscular hemoglobin (MCH)• Mean corpuscular hemoglobin concentration (MCHC)• Platelet count

White Blood Cell Count and DifferentialWBCs defend the body from bacteria and viruses. The normal range for a WBC count is 4,300 to 10,800/mm3. A patient’s WBC count can be determined by use of an automated cell counter. Most common automated cell counters are not CLIA waived and not in the scope of practice for the medical assistant.

Patients with low WBC counts may be susceptible to infections.

To view WBCs, a drop of blood is smeared on a glass slide and then stained so that they can be seen with a microscope. From the smear, the types of WBCs are counted and reported by type. This count is known as the WBC differential. WBC differentials are not CLIA waived.

The WBC types and their approximate percentage of the WBC count include the following:

• Neutrophils = 59%• Lymphocytes = 34%• Monocytes = 4%• Eosinophils = 2%• Basophils = 1%

Red Blood Cell CountRBCs are counted by hematology cell counter instru-ments. Anemia can be caused by a low RBC count (as in iron defi ciency)or blood loss. The normal range of RBCs for men is 4.6 to 6.2 million/mm 3; for women, it is 4.2 to 5.4 million/mm3.

When the WBC differential is counted on the blood smear, RBC morphology or appearance is evaluated and reported. This report contains comments on the variation classifi cations that appear due to the disease conditions:

• Variations in size• Variations in shape• Alterations in color• Alterations in how the RBCs are spread out on the

blood smear

HemoglobinHemoglobin contains four chains called globins. Defects in the globin chains cause abnormal hemoglobins. Sickle cell anemia is caused by a defective globin chain. Iron is found in the globin and gives RBCs their red color. The normal range for hemoglobin is 13 to 18 g/dL (or g/100 mL) in men and 12 to 16 g/dL in women. Measuring the hemo-globin is used to diagnose anemia. There are also point-of-care (POC) methods approved for use by medical assistants. An example is the HemoCue System Hemoglobin Plasma/Low Hemoglobin Analyzer.

The hematocrit is the percentage of RBCs in whole blood. Microhematocrit tubes are collected and spun in a special microcentrifuge to separate the cells from the plasma. After the tubes are spun, they are measured to determine the percentage of RBCs present.

The purpose of measuring the hematocrit is also to detect types of anemia. The normal range is 45% to 52% in men and 37% to 48% in women.

Erythrocyte IndicesErythrocyte indices, MCV, MCH, and MCHC are cal-culations. The hematology cell counter measures the size of the RBCs and how much hemoglobin they hold. The calculations help diagnose and treat anemias. There are different types of anemia, and knowing the type is required to plan a treatment. The MCV, MCH, and MCHC help identify the actual type of anemia.

Mean Cell Volume

The MCV is the average size of the RBCs in categories:

• Normal-size cells are called normocytic.• Smaller-size cells are called microcytic.• Larger-size cells are called macrocytic.

The MCV can indicate anemias caused by nutritional defi ciencies. The normal range for MCV is 80 to 95 fL.

Microcytosis (MCV below 80 fL) indicates iron defi ciency.

Macrocytosis(MCV above 95 fL) indicates defi ciency of vitamin B 12 and folate.

Mean Cell Hemoglobin and Mean Cell Hemoglobin Concentration

RBCs with inadequate amounts of hemoglobin are termed hypochromic. The MCH calculation measures the amount of hemoglobin in a single RBC. The normal range for MCH is 27 to 31 picograms.

The MCHC is the average amount of hemoglobin per RBC. The normal range for MCHC is 32 to 36 g/dL. MCHC is decreased in the same conditions as the MCV.

Decreased MCHC values, termed hypochromia, may be due to:

• Iron defi ciency anemia• Thalassemia• Blood loss• Vitamin B6 defi ciency

There are disorders in which the MCV and the MCHC differ: in an anemia called pernicious anemia, the MCV is high, but the MCHC is normal.

Platelet CountThe normal range for platelets is 200,000 to 400,000/mm3. Low platelet counts are associated with increased bleeding. The bleeding is usually from many small capillaries. The normal values are required to be listed for each result on the report.

Erythrocyte Sedimentation RateThe ESR measures how quickly RBCs settle out in a tube. The blood is placed in a specially made tube and allowed to settle undisturbed for 1 hour. At the end of the hour, the distance the RBCs have fallen is measured. The method used in POLs to measure ESR is called the Westergren method. Other methods have a much higher risk of exposure to blood. The Wester-gren method has a closed system that reduces the medical assistant's exposure to the patient's blood.

Always verify the following conditions to ensure accurate ESR results:

• Test should be started within 2 hours of specimen col-lection.

• Test should be conducted at room temperature.• The blood column must contain no bubbles.• The tube must remain completely vertical during testing.

• The sedimentation rack must be placed on a counterwith no vibrations. (Do not place near a centrifuge.)

• The sedimentation rack must be away from all draftsand direct sunlight.

• Test results should be read at exactly 60 minutes.

The normal range for men is 0 to 10 mm/hr, and for women, it is 0 to 20 mm/hr. ESR values do not diag-nose a specifi c disease. They measure how much infl am-mation is present in the body. The more rapidly the RBCs fall in the tube, the more infl ammation is pres-ent. An example of a disease monitored by the ESR is fi bromyalgia.

Coagulation (Hemostasis) TestsThe two most common laboratory coagulation tests are the prothrombin time (PT) and the partial thromboplas-tin time (PTT). There are waived testing analyzers for measuring the PT.

Prothrombin TimeThe patient’s PT is measured by adding two reagents to the patient’s specimen. If the substances were inside the body, they would start a clot. Adding the substances to the blood and measuring the clotting time gives a PT result. The normal range is 12 to 15 seconds, but each laboratory establishes its own range. This is the test used to monitor a patient taking Coumadin™.

The PT is reported along with an international normalized ratio (INR). The INR is a standardized result. The INR is a calculation from the patient’s PT result and a reference standard. The INR is reported because it is similar from lab to lab. PT results can very a lot from lab to lab. The INR will be comparable in any lab the patient might choose.

Partial Thromboplastin TimeThe PTT test is similar to a PT test. The same reagents are added to the patient’s specimen. This time, how-ever, they are added in a different sequence with an incubation period in between. The clotting time is then determined. The normal range is 32 to 51 seconds, but each laboratory establishes its own range, so there may be a slight variation. The PTT test identifi es differ-ent factor defi ciencies than the PT test. A hemophilia patient will have a long PTT time because of its missing coagulation factor.

Coagulation Factor LevelsThe body uses several coagulation factors to successfully clot blood. When a patient has a bleeding problem, the coagulation factors can be measured to identify if one of them is low. In some cases, the coagulation factor can be added to the patient’s blood to restore normal clotting. Periodic replacements may be required to maintain the normal level. Coagulation factors are usually measured after a patient has an abnormal PT or PTT result.