Medical Assistant Exam: Clinical Procedures - Performing Selected (Medical) Tests

Once a specimen is collected, the tests performed on it reveal a whole range of factors relating to health status and disease. This section describes the tests that are performed with specimens collected, and the purpose of those tests.

Urinalysis
A physiologic change in the body caused by disease can create a disturbance in one or more of the functions of the kidney. Detection of such a disturbance can be made with the examination of urine and other body fluids.

Physical Urinalysis
The physical examination of urine includes determination of the color, appearance, and specific gravity. The color and appearance of the urine specimen may be evaluated during preparation for another testing procedure, such as the chemical testing of the urine or before centrifugation of the specimen in preparation for microscopic analysis.
Color: The following list describes aspects of the color of urine that should be noted.

- The normal color of urine ranges from almost colorless to dark yellow.
- Dilute urine tends to be a lighter yellow in color while concentrated urine is a darker yellow.
- The color of the urine is the result of the presence of a yellow pigment known as urochrome, which is produced by the breakdown of hemoglobin.
- Classifications that are used to describe the color of urine include light yellow, yellow, dark yellow, light amber, amber, and dark amber.
- Abnormal colors may be caused by the presence of hemoglobin or blood, bile pigments, and fat droplets.
- Some foods and medications can also cause the urine to change color.

Transparency: The transparency or clarity of urine is usually examined at the same time as the color evaluation. Fresh urine is usually clear, or transparent, but becomes cloudy as time goes by. Cloudiness in a urine sample may be the result of the presence of bacteria, pus, blood, fat, yeast, sperm, mucous threads, or fecal contamination. Classifications used to describe the appearance of urine include clear, slightly cloudy, cloudy, and very cloudy.

Specific gravity of urine measures the weight of the urine compared with the weight of an equal volume of distilled water. Specific gravity indicates the amount of dissolved substances present in the urine, providing information on the ability of the kidneys to dilute or concentrate the urine. Acceptable values are:
- normal range: from 1.003 to 1.030
- usual range: from 1.010 to 1.025

The reagent strip method is the most common method used to measure specific gravity. It involves a color comparison determination using a reagent strip that contains a reagent for specific gravity. The reagent strip is dipped into the urine specimen and the results are compared with a color chart.

Chemical Examination of Urine
Substances present in excess amounts in the blood are usually removed by the urine. The chemical testing of urine is an indirect means, therefore, of detecting abnormal amounts of chemicals in the body. The chemical examination of urine can also be used to detect the presence of blood and nitrite.
Chemical tests that are routinely performed during a urinalysis include testing for pH, glucose, protein, and ketones. Other chemical tests that may be performed include testing for blood, bilirubin, urobilinogen, nitrite, and leukocytes.

Urine analysis is broken down into two general categories:
- Qualitative analysis of urine indicates whether a substance is present in the urine and also provides an approximate indication of the amount of the substance present. The interpretation of qualitative tests usually involves the use of a color chart, with results recorded in terms of trace, 1+, 2+, or 3+; trace, small, moderate, or large; or negative or positive.
- Quantitative analysis of urine indicates the exact amount of a chemical substance that is present in the body; the results are reported in measurable units.

The most important tests performed on urine examine the following elements:
- pH: The pH level indicates the acidity or alkalinity of a solution. The pH scale ranges from 0.0 to 14.0. The lower the number, the greater the acidity; the higher the number, the greater the alkalinity. A pH reading of 7.0 is neutral; a reading below 7.0 indicates acidity; and a reading above 7.0 indicates alkalinity.
- Glucose: No glucose should be detected in urine. Glucose in the blood is filtered through the nephrons and is reabsorbed into the body. If the glucose concentration is the blood becomes too high, the kidney is unable to reabsorb all of it back into the blood, the renal threshold is exceeded, and glucose is spilled into the urine; this is called glycosuria.
- Protein: Protein in urine (proteinuria) usually indicates a pathological condition if found in several samples over time. Some of the conditions that may cause proteinura include glomerular filtration problems, renal disease, or bacterial infection.
- Ketones: Ketones are the normal products of fat metabolism and can be used by muscle tissue as a source of energy. When large amounts of fat are metabolized by the body, the muscles cannot handle all of the ketones that result. Large amounts of ketones accumulate in the tissues and body fluids; this condition is called ketosis. The body rids itself of these excess ketones in the urine. This is called ketonuria. Conditions that may lead to ketonuria include uncontrolled diabetes mellitus, starvation, and a diet composed almost entirely of fat.
- Bilirubin: Bilirubin is the breakdown of hemoglobin. Bilirubin is normally transported to the liver and excreted into the bile; eventually, it leaves the body through the intestines in the feces. Certain liver conditions, such as gallstones, hepatitis, and cirrhosis, may result in the presence of bilirubin in the urine. This is called bilirubinuria.
- Urobilinogen: Urobilinogen is normally excreted by the liver into the intestinal tract. Bacteria present in the intestines convert it to urobilinogen. Most urobilinogen is excreted in the feces. Conditions such as excessive hemolysis of red blood cells, infectious hepatitis, cirrhosis, congestive heart failure, and infectious mononucleosis may increase the urobilinogen levels in urine.
- Blood: Blood is not normally found in urine (unless it is present as a contaminant during menstruation). Blood in urine is called hematuria. Hematuria may be the result of an injury or disorder such as cystitis, tumors of the bladder, urethritis, kidney stones, and certain kidney disorders.
- Leukocytes: Leukocytes found in urine is known as leukocyturia. Leukocytes found in the urine indicate an inflammation of the kidneys and the lower urinary tract.
- Nitrate: Nitrate is a compound of nitrogen and oxygen found in many food items. Some pathogenic bacteria posses the ability to convert nitrate to nitrite. Nitrite in the urine suggests the presence of these pathogenic bacteria and indicates a possible urinary tract infection.

Reagent strips are commonly used to test the urine in the medical office. The number and type of reagent areas included on the reagent strip depend on the particular brand of reagent strips. For instance, Multistix 10 SG strips contain ten reagent areas for testing pH, protein, glucose, ketones, bilirubin, blood, urobilinogen, nitrite, specific gravity, and leukocytes.
The chemical testing of the reagent strip can be performed manually by placing the reagent strip in the urine and, at a certain time period, comparing the color on the reagent strip to the values on the container. A urine analyzer is used to perform an automatic chemical examination of urine with reagent strip. The reagent strip is fed into the machine and prints out the results.

Microscopic Urinalysis
The microscopic exam is a method used to confirm the results of the physical and chemical urine evaluation. The medical assistant can prepare the urine for microscopic examination, but a physician or other qualified healthcare professional must read and record the results.
Substances that may be found in the microscopic urine include RBCs, WBCs, epithelial cells, crystals, bacteria, and other substances.

Hematology
Hematology is the study of blood, including the morphologic appearance and function of blood cells and diseases of the blood and blood-forming tissues. Laboratory analysis in hematology examines blood for the purpose of detecting pathologic conditions. Hematology testing also includes blood cell counts, evaluating the clotting ability of the blood, and identifying cell types.

The most frequently performed hematology test is the complete blood count (CBC). The tests included in the CBC are:
- red blood cell count (RBC)
- white blood cell count (WBC)
- platelet count
- hemoglobin (Hgb)
- hematocrit (Hct)
- differential WBC count (diff)
- RBC indices

Hematologic laboratory tests can now be performed in the medical office, due to advances in automated blood analyzers designed for use in the medical office. Automated blood analyzers provide accurate test results in a short time.

Red Blood Cell
Red blood cells, the most common type of cell in the blood, are responsible for delivering oxygen to the body. The RBC count is a measurement of the number of RBCs in whole blood.

ACCEPTABLE RANGES FOR RBC COUNT

Category

Normal Range
Normal as Expressed on Lab Reports

healthy woman
4 to 5.5 million/cubic mm of blood
4 to 5.5 (x106/mm3)

healthy man

4.5 to 6.2 million RBCs/cubic mm of blood

4.5 to 6.2 (x106/mm3)

Abnormal levels in RBC count can result from several factors or conditions.
- decrease in the RBC count: anemia, Hodgkin’s disease, and leukemia
- increase of RBCs: polycythemia, dehydration, and pulmonary fibrosis

White Blood Cell
White blood cells play a major role in the immune system. There are five types of white blood cells (or leukocytes), each having a certain size, shape, appearance, and function:
- neutrophils
- eosinophils
- basophils
- lymphocytes
- monocytes

The purpose of the differential cell count is to identify and count the five types of WBCs in a representative blood sample. An increase or decrease in one or more types may occur in pathologic conditions, which may assist the physician in making a diagnosis.
The differential cell count can be performed automatically or manually. The automatic method is faster and more convenient.

Automatic method: This procedure involves the use of a blood cell counter, such as the Coulter cell counter. Specimen requirements: an ethylenediaminetetraacetic acid (EDTA) anticoagulated blood specimen, which is obtained through venipuncture. The blood cell counter automatically performs the differential count and the results are printed on a laboratory report.

Manual method: This procedure requires that the medical assistant make two blood smears. Some pointers on preparing the blood smears follow.
- Blood smears should be made within two hours of the specimen collection.
- After preparing the blood smear, the medical assistant places the slides in a protective container for transport to an outside laboratory.
- Because WBCs are clear and colorless, they must be stained first with an appropriate dye (usually Wright’s stain) before a differential count is performed. The nucleus, cytoplasm, and any granules in the cytoplasm take on the characteristic color of their cell type, which aids in proper identification.
- A minimum of 100 WBCs is identified on the blood smear and each is identified as one of the five types of leukocytes and the number of each type is translated into a percentage.This then reflects the overall distribution of WBCs in the patient’s bloodstream.

The normal range for each type of WBC making up the total number of leukocytes is:
- neutrophils: 50% to 70%
- eosinophils: 1% to 4%
- basophils: 0% to 1%
- lymphocytes: 20% to 35%
- monocytes: 3% to 8%

Platelets: Platelets are colorless cell fragments that play a vital role in blod clotting. The platelet count, also part of the CBC, assists in evaluation of bleeding disorders that occur with liver disease, thrombocytopenia, uremia, and anticoagulant therapy.
Normal ranges for platelet counts are: 150,000 to 400,000 per cubic millimeter.

Hematocrit
A hematocrit test involves separating the components of the blood. The solid or cellular elements are separated from the plasma in a blood specimen that has been prepped with an anticoagulant and put through a centrifuge.
- bottom layer: heavier RBCs packed together
- top layer: clearer, lighter plasma, which is straw-colored
- middle layer: yellowish gray layer that holds the platelets and WBCs; called the buffy coat

The purpose of the test is to determine the percentage volume of RBCs in whole blood. The normal hematocrit ranges are 37% to 47% for women and 40% to 54% for men.
A low hematocrit reading may indicate anemia and a high reading may indicate polycythemia.
The microhematocrit method is used most often in the medical office to perform a hematocrit. Capillary blood is drawn directly from a skin puncture into a capillary tube lined with an anticoagulant agent. After collecting the specimen, one end of the capillary tube is sealed and the tube is placed in a microhematocrit centrifuge. The centrifuge spins the blood at an extremely high speed. Within one to three minutes, the RBCs are packed and the results can be read.

Hemoglobin
Hemoglobin is a major component of RBCs. It carries oxygen to the tissue cells of the body and is responsible for the color of the RBCs. It therefore can be used to measure the oxygen-carrying capacity of the blood. The normal ranges are 12 to 16 g/dL for an adult female and 14 to 18 g/dL for an adult male.
A hemoglobin determination is performed as an individual test or part of the CBC, with either capillary or venous blood.

A decreased hemoglobin level can indicate several conditions, including:
- anemia
- hyperthyroidism
- cirrhosis
- severe hemorrhaging
- hemolytic reactions
- certain systemic disease such as leukemia and Hodgkin’s disease

Increased levels of hemoglobin can indicate several conditions, including polycythemia, chrronic obstructive pulmonary disease, and congestive heart failure.
The most accurate and dependable technique for measuring hemoglobin levels involves the use of a blood analyzer.

Erythrocyte Sedimentation Rate (ESR)
The erythrocyte sedimentation rate is a screening tool to analyze inflammatory processes. An increased ESR can indicate a range of conditions: It can be a sign of a simple bacterial infection, or a sign of an autoimmune disease such as systemic lupus erythematosus, rheumatoid arthritis, or Crohn’s disease.

The ESR test consists of placing a well-mixed anticoagulated blood sample in a tube for one hour to measure how fast the RBC settle to the bottom. Normal RBC are biconcave-shaped and settle at a steady rate. Conditions in which the RBC are abnormal in shape, such as sickle-cell anemia, or conditions that affect the amount of fibrinogen in the plasma, such as hypofibrinogenemia, can change the sedimentation rate.
There are automated tools for performing ESR testing; however, the test is usually performed manually using either the Westergren method or Wintrobe method.

Westergren method: A sample of venous blood is mixed with a 3.8 percent sodium citrate solution (an anticoagulant agent) and left to stand vertically for an hour. The ESR is measured in millimeters of sediment that forms in one hour (mm/hr).

Normal ranges ESR using the Westergren method are:
- Males: 0–9 mm/hr
- Females: 0–20 mm/hr
- Children: 0–13 mm/hr

Potential sources for error using the Westergren method are incorrectly mixing the solution, disrupting the tube during the test, or not placing the stand level.

Wintrobe method. A sample of venous blood is thoroughly mixed with EDTA anticoagulant and then transferred to a Wintrobe tube. The tube is filled with 1 mL of blood and set vertically in a rack and left to stand for one hour.

Normal ranges for ESR using the Wintrobe method are:
- Males under 50: 0–15 mm/hr
- Males over 50: 0–20 mm/hr
- Females under 50: 0–20 mm/hr
- Females over 50: 0–30 mm/hr
The potential sources of error in the Wintrobe method include a dirty Wintrobe tube, disturbances during the test, the rack and tube not being level, and a blood specimen that was not mixed well.

Coagulation
Coagulation studies measure the ability of blood to clot. A prolonged coagulation time makes a person less likely to develop blood clots, especially after heart bypass surgery, heart valve replacement surgery, or any other procedure that disrupts the normal smooth lining of the arterial wall lining of the heart.
All patients on anticoagulant medication therapy need to have the blood monitored regularly for its clotting ability. The aim of anticoagulation therapy is to prolong the amount of time it will take for blood to clot, without making that time so long that the person has excessive bleeding. The goal is to make the length of time it takes to clot three times longer than normal.

Anticoagulation therapy is also used on a person who has a history of blood clots, such as thrombophlebitis, and to prevent heart attack or stroke in individuals with significant risk factors.

There are 12 coagulation factors in human plasma that are involved in clot formation. Formation of a clot has been further subdivided into two pathways.
- Extrinsic system: The clotting factors involved in this system are dependent on vitamin K for their production.
- Intrinsic system: The clotting factors involved in this system are NOT dependent on vitamin K for their production.

The two coagulation studies performed most frequently are:
- prothrombin time (PT), which measures extrinsic pathway factors; it is a measure of the clotting ability of the blood and can help diagnose problems with bleeding.
- partial thromboplastin time (PTT), which measures intrinsic pathways.

Prothrombin time (PT): Used to monitor patients receiving warfarin (Coumadin) therapy. Because prothrombin is produced in the liver, liver disease can also cause an increase in PT, which puts the patient at risk for bleeding episodes.
The normal PT for patients not taking warfarin is between 11 and 14 seconds. The range for individual patients taking warfarin should be established by the physician.

Partial thromboplastin time (PTT): The screening test for hemophiliacs (people whose blood does not clot or clots slowly) who are deficient in factor VIII (hemophilia A) or factor IX (Christmas disease). The PTT is also the most common coagulation test for assessment of heparin therapy. Normal ranges should be established for each laboratory, but they are usually between 30 and 45 seconds.

The PTT is a two-stage test, requiring two reagents: contact factor and phospholipid. The procedure for using each brand of analyzer is different. The medical assistant should be sure to follow the manufacturer’s directions.

Blood Chemistry
Blood chemistry involves quantitative measurements of all chemical substances in the circulating blood and other body fluids. Common chemistry blood tests include glucose, hormones, lipids, drugs, and antibodies.
Chemistry testing can be done on an analyzer or individual test kits.

Glucose
When carbohydrates are digested, simple sugars such as glucose are generated. Glucose travels from the bloodstream to provide energy to the body’s cells and tissues. The body produces two hormones that aid in the regulation of blood glucose levels: insulin and glucagon. Glucagon converts the stored glucose levels into glucose when blood glucose levels become low. The pancreas releases insulin to facilitate the transport of glucose from the bloodstream to the tissues and cells, thus lowering blood glucose levels.
A fasting glucose is the term applied to testing for glucose levels when a patient has been fasting (nothing ingested except for water) for 12 hours. The fasting glucose normal values are 70–100 mg/dL.

Glucose monitoring can easily be done in the medical office. Many glucose monitors are available to patients to monitor their glucose at home.

Kidney Function Tests
BUN—or blood urea nitrogen—is a test of how well the kidneys are functioning.
Urea nitrogen is produced as a waste product in the process of metabolizing proteins. It forms in the liver and travels via the bloodstream to the kidneys to be excreted. Since the kidneys are involved in the elimination of urea from the body, testing the level of urea nitrogen is one way to understand how well the kidneys are functioning.
One potential problem in using BUN as a test for kidney function, however, is that other causes, such as problems with the liver, can lead to changes in the levels of urea nitrogen.

Liver Function Tests
The liver is a multipurpose organ whose many functions include detoxification, protein synthesis, and production of bile, which aids in digestion. The tests associated with liver function measure proteins or enzymes in the blood that are involved in the operation of the liver. The levels of these substances, therefore, are a window into liver function. Standard liver function tests (LFTs) include:
- Bilirubin: This test measures how bilirubin, which is a waste product of the hemoglobin in the blood, is cleared from the blood by the liver.
- Albumin: This test measures the level of albumin, which is a protein manufactured by the liver.
- ALT and AST: These two indicators—alanine aminotransferase (ALT) and aspartate aminotransferase (AST)—are enzymes associated with liver cells; the level of both enzymes are raised when the liver is damaged; since AST elevations may be caused by diseased organs other than the liver, ALT is used a more targeted indicator for inflammation of the liver.
- ALP and GGT: These two indicators—alkaline phosphatase (alk. phos.) and gamma-glutamyl transpeptidase (GGT)—are also enzymes, in this case associated with the liver, in particular the bile ducts, or channels within or outside the liver; elevated levels can indicate obstruction in the bile ducts.

Lipid Profile
Lipids are fats or fatlike substances that do not dissolve water. Lipids provide an alternative energy source. Blood lipids that are responsible for cardiovascular disease are classified as lipoproteins. Lipoproteins are complex molecules made of fats attached to proteins. Two important types of blood lipids are cholesterol and triglycerides.
Cholesterol: An important component of cell membranes, cholesterol is used in the production of hormones and bile. Most of the cholesterol circulating in the body is manufactured by the liver. A portion of cholesterol—known as dietary cholesterol—comes from an individual’s diet.
High cholesterol means that there is excessive amount of cholesterol in the blood called hypercholesterolemia. High cholesterol may cause fatty deposits, or plaque, to build up on the walls of the arteries, a condition known as atherosclerosis. As the atherosclerosis progresses, the arteries become more occluded, or blocked, which can eventually lead to a heart attack or stroke.

Cholesterol is transported in the blood as a complex molecule known as a lipoprotein. Two types of lipoproteins contain cholesterol:
- Low-density lipoprotein (LDL)—known as 'bad cholesterol' since an excess amount of it in the blood can cause plaque to build up on the arterial walls. LDL comes from ingested fats and from the liver. It is delivered to the blood and to the muscles where it is deposited on the cells.
- High-density lipoprotein (HDL)—known as the 'good cholesterol' since HDL removes excess cholesterol from the cells and carries it to the liver to be excreted. A high HDL has been shown to reduce the risk of heart disease. A low HDL is a risk factor for coronary heart disease.

Triglycerides. The most common form of fat in the body and food, they are a major source of energy in the body. When calories are ingested, but not used immediately, the body converts the excess to triglycerides, which are then stored in fat cells. Through the action of hormones, triglycerides are released from fat tissue to provide energy to the body between meals.

Hypertriglyceridemia, a condition marked by excess levels of triglycerides in the blood, can cause coronary artery disease through a buildup of lipoprotein at the artery walls, as in conditions of high cholesterol. Other conditions, however, such as diabetes mellitus, can result in increased levels of triglycerides; therefore, care must be taken in a diagnosis. A lipid profile includes:
- total cholesterol
- HDL cholesterol
- LDL cholesterol
- triglycerides

Because triglyceride levels are affected by the consumption of food, the patient must be instructed to fast for at least 12 hours before collection of the blood specimen.

Hemoglobin A1c
Hemoglobin is part of the red blood cells; it transports oxygen in the body and helps to process glucose and monitor diabetes.
When an individual consumes food containing glucose, the circulatory system absorbs the glucose from the digestive tract. Glucose tends to bind to protein, including a protein that makes up hemoglobin. When glucose attaches, or is glycosylated, to this protein, it forms hemoglobin A1c.
Therefore, when a diabetic patient’s blood sugar is too high, the hemoglobin A1c rises: It builds up and combines with hemoglobin—that is, it becomes glycated, producing increased amounts of A1c. By measuring a patient’s homoglobin A1c level, then, the medical assistant—and the patient—will be able to monitor the blood sugar level and therefore the status of the patient’s diabetes.

Immunology
Immunology is the study of the immune system. It deals with antigen and antibody reactions.
- Antigen—a substance that is capable of stimulating the formation of antibodies in an individual. Antigens may consist of protein, glycoprotein, complex polysaccharides, or nucleic acid. Some examples of antigens include bacteria and viruses, bacterial toxins, allergens, and blood antigens.
- Antibody—produced by the body in response to it being invaded by an antigen. Antibodies are capable of combining with antigens, resulting in antigen-antibody reactions.
Laboratory testing in immunology deals with the study of antigen-antibody reactions to assess the presence of a substance or to assist in the diagnosis of a disease.

Mononucleosis Test
Mononucleosis is an acute infectious disease commonly seen in children and young adults. It is caused by the Epstein-Barr virus (EBV). Its symptoms include:
- sore throat
- fatigue
- lymphadenopathy
- splenomegaly

A patient with symptoms of mononucleosis will have a mono test, as well as other clinical testing including a CBC and liver enzymes.
The rapid mono test is usually be performed in a medical office. Most mononucleosis tests do not look for EBV, but rather test for heterophile antibodies, which are sometimes present when a patient is infected with EBV.

Strep Test
The most common streptococcal condition is streptococcal sore throat, or streptococcal pharyngitis, which usually affects children and young adults and is caused by a Group A beta-hemolytic streptococcus known as Streptococcus pyogenes. Streptococcal pharyngitis is a potentially serious condition because some patients develop a sequela condition. A sequela is a morbid secondary condition that occurs as a result of a less serious primary infection. A sequela of streptococcal infection is rheumatic fever.
Rapid streptococcus tests directly for group A streptococcus from a throat swab in a very short time. Most tests only take about four to ten minutes. The most frequent streptococcus test is the direct antigen identification test, which confirms the presence of group A streptococcus through an antigen-antibody reaction. The test works by combining particles sensitized to the streptococcus antibody with the throat specimen. If group A streptococcal antigen is in the specimen, it combines with the antibody-sensitized particles to produce a color change that can be observed. Rapid streptococcus test kits also include a control that determines whether the test results are accurate.

C-Reactive Protein (CRP)
During inflammation and tissue destruction, an abnormal protein called C-reactive protein (CRP) appears in the blood. Patients with inflammatory conditions or disorders accompanied by tissue destruction have positive results to this test.
CRP rises during systemic inflammation and is used in testing for such illnesses as rheumatoid arthritis and lupus. It also may be an additional method of evaluating a patient’s risk for cardiovascular disease.

Pregnancy Testing
Pregnancy testing, which is based on immunological principles, relies on the detection of the human chorionic gonadotropin (HCG) hormone, which is secreted by a fertilized egg. HCG levels can be detected from urine or serum.
The serum radioimmunoassay test for HCG is used to detect HCG in blood serum. This test can detect pregnancy earlier and with more accuracy than a urine pregnancy test. A serum pregnancy test can usually detect pregnancy at approximately the eighth day after fertilization.
Immunoassay tests provide for the rapid, qualitative detection of HCG in urine and blood. The immunoassay testing takes about five minutes to perform. The results are observed by a color change if the results are positive. If the the antibody in the sample contains the antigen, then a color change will appear in the kit, indicating a positive result.

Microbiology
Microbiology is the scientific study of microorganisms and their activities. Microorganisms are tiny living plants and animals that cannot be seen by the naked eye, but can be viewed under a microscope.
An infectious disease is one in which a microorganism is transmitted directly or indirectly between individuals, causing infection. Sources of human infection include other humans, animals, and sometimes the soil.

Bacteria
Bacteria are microscopic unicellular organisms that do not have a nuclear membrane enclosing their genetic material. Bacteria are classified into three basic groups based on their shape: cocci (round), bacilli (rod-like), and spiral bacteria. More information about bacteria can be found in the first section of this chapter, under Types of Pathogenic Microorganisms.

The Gram Stain Method of Classifying Bacteria
The Gram stain, named for the Danish scientist who developed the technique, is the most basic method for, and usually the first step in, identifying bacteria. Testing the chemical and physical qualities of the bacteria’s cell walls, the Gram stain classifies bacteria into two groups: gram-positive or gram-negative.
A bacterium tests as gram-negative or gram-positive according to the ability of its cell wall to either retain or lose color through decolorization. This identification of gram-negative or gram-positive aids in identification of an organism.
Bacteria that are Gram-stained are observed for their characteristic shape and fall into one of the following categories: gram-positive rods, gram-negative rods, gram-positive cocci, or gram-negative cocci.

Gram-Positive Diseases -   Gram-Negative Diseases

Gram-positive infections include methicillin-resistant Staphylococcus aureus (MRSA), strep infections, and toxic shock. 
Gram-negative infections include salmonella, pneumonia, urinary tract infections, and gonorrhea.

The Gram stain technique is a four-step process:

1. First, a primary stain—crystal violet—is used. This stains the culture purple.

2. Iodine then is applied to 'hold' the stain.

3. This is then followed by the application of a decolorizer, alcohol-acetone, which removes the purple color.

4. Finally, a counterstain, usually safranine, is applied.

When stained according to the manufacturer’s directions, the gram-positive bacteria stain purple and the gram-negative stain pink/red.

Parasites
Parasitology includes the study of all parasitic organisms that live on or in the human body. In parasitic relationships, the host is harmed as the parasite thrives. Parasites are transmitted by ingestion during the infective stage, direct penetration of the ingestion during the infective stage, direct penetration of skin by infective larvae, or inoculation by an arthropod vector. It is not possible to identify a parasite accurately on the basis of a single test or specimen. Most parasites are identified in urine, sputum, tissue fluids, or tissue biopsy samples.
Helminths. Helminths are parasitic worms. They live on or within another living organism and nourish themselves at the expense of the host organism. They can live in animals or humans and are usually transmitted through the soil, by infected clothing, or through contaminated food or water. Helminths go through the same life cycle as other worms. The adult worm lays eggs (ova). The ova develop into larvae. Larvae grow into adult worms, which lay eggs, and the cycle begins again. Diagnosis is usually based on microscopic examination of feces for ova and parasite and the patient’s signs and symptoms.

Other Microorganisms
Other pathogenic microorganisms include virus, fungus, and protozoa.

Tuberculosis Testing
The Mantoux test is used to test for tuberculosis. The Mantoux test is administered through an intradermal injection using a tuberculin syringe. It is important that the medical assistant draw up the proper amount of tuberculin solution.
- Injecting too much of the solution might trigger a reaction not caused by a tuberculous infection.
- Injecting too little of the solution results in insufficient solution being injected into the skin to cause a reaction. This will invalidate the test because if no reaction occurs, it cannot be accepted as a negative reaction.

The medical assistant must inject the solution properly:
- The injection must be made into the intradermal layers of the skin to form a wheal.
- If the injection is made into the subcutaneous layer, a wheal does not form.
- If the injection is too shallow, the injection may cease leakage of the tuberculin solution onto the skin.

Once the test has been administered, the results must be read within 48 to 72 hours. The medical assistant should use inspection and palpation to read the test results. If induration, or hardening, is present, the medical assistant should rub his or her fingers lightly from the area of normal skin to the indurated area to assess its size. The area of induration should be measured in millimeters.
The extent of induration is the only criterion used to determine a positive reaction. If erythema, or redness, is present without induration, the result is negative. The diameter of induration should be measured horizontally to the long axis of the forearm, and the results should be recorded in millimeters. If no induration is present, 0 mm should be recorded.

The following reactions might indicate tuberculous infection:
- The formation of vesicles, or fluid-containing lesions of the skin. If vesicles are present, the test is interpreted as strongly positive and warrants further diagnostic procedures to determine whether active TB is present.
- Induration of 10 mm or more constitutes a positive reaction and warrants further diagnostic procedures to determine active TB is present.
- Induration of 5 mm should be interpreted as a positive reaction for an individual who lives in close contact with a person with infectious TB, an HIV infected individual, or an individual at risk for HIV but whose HIV status is unknown.
- A doubtful reaction is an induration measuring 5 mm to 9 mm. Retesting is recommended using a different site of injection.
- A negative reaction is an induration less than 5 mm.

Guaiac (Occult Blood) Testing
The guaiac (occult blood) test screens patients for the presence of occult blood, which is blood present in the feces but not visible to the eye. Blood in the stool can indicate a number of conditions, including hemorrhoids, diverticulosis, polyps, colitis, upper gastrointestinal ulcers, and colorectal cancer, which is one of the most common cancers in people above the age of 40.
The test assesses the presence of blood in stool specimens collected from bowel movements on three different days. The purpose of using three specimens is to provide for the detection of blood from gastrointestinal lesions that exhibit intermittent bleeding. The patient must collect the specimens at home and return the prepared slides to the medical office for developing. The medical assistant is responsible for providing the patient with instructions on collection and proper care and storage of the slides until the slides are returned to the medical office.
The patient must follow a special high-fiber, meatless diet beginning three days before the guaiac slide test and continuing until all three slides have been prepared. Meat contains animal blood that could lead to a false-positive test result, and a diet high in fiber encourages bleeding from lesions that may bleed only occasionally. In addition, fiber adds bulk, which promotes bowel movement.
The medical assistant should perform a quality control procedure after the patient’s slide test has been developed, read, and interpreted.
Although the primary use of the guaiac slide test is to screen for colorectal cancer, other important uses of this test include screening for an upper GI ulcer or for disorders casing gastric and intestinal irritation. A positive test results on the guaiac slide test indicates blood in the stool, although the cause of the bleeding still must be determined.

Medical Imaging
While a medical assistant cannot take X-rays, he or she must be capable of preparing a patient for a medical imaging exam and must be informed of the safety procedures associated with this X-ray technology.

Safety Measures
Both the person performing the X-ray procedure and the patient need protection against excessive radiation or radiation reaching parts of the body to which radiation is a danger, such as the reproductive organs and thyroid.

Some of the protective equipment needed includes:
- gloves
- lead apron that reaches below the waist to protect the internal organs of the trunk and the reproductive organs of both women and men
- goggles
- leaded neck protector to shield the thyroid
The X-ray technician also stays as far away from the X-rays as possible, stepping out of the room or behind a lead-lined barrier while the X-ray machine takes the image. The technician is also responsible for the proper working of the X-ray machine to ensure that it does not emit excess radiation.

Patient Preparation and Instruction
Patient preparation for routine radiography involves several instructions and precautions:
- The outer clothing that covers the radiographed are should be removed; a gown should be provided if appropriate.
- No metal objects should be included in the radiation field because these items will appear as artifacts on the images. This includes jewelry, zippers, snaps, and other clothing fasteners; underwire bras; and the contents of pockets.
- Nonmetal objects that are thick or heavy should also be removed. Buttons and the heavy seams in jeans are examples of other clothing items that can cause artifacts on radiographs if they are in the imaging field.
The patient must remain still while the exposure is made. If more than one exposure is needed, the film is changed, the patient is repositioned, and the steps are repeated until the examination is complete.