Patient's Guide to Medical Tests: Everything You Need to Know about the Tests Your Doctor Prescribes

Patient's Guide to Medical Tests: Everything You Need to Know about the Tests Your Doctor Prescribes

by Joseph C. Segen


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Patient's Guide to Medical Tests: Everything You Need to Know about the Tests Your Doctor Prescribes by Joseph C. Segen

The Patient's Guide to Medical Tests, Second Edition provides a basic understanding of the diagnostic procedures and tools used by physicians, hospitals, and commercial laboratories. Organized alphabetically, this comprehensive guide presents information on more than 1,000 commonly prescribed tests and procedures. Each entry includes a description of the test, patient preparation required, a description of the procedure itself, the reference range, what abnormal values may signify, and the approximate cost of each test. An extensive glossary of medical terms translates professional terminology into accessible language, as does an appendix of medical abbreviations and symbols. New and updated coverage includes information on which tests have been "retired" as well as new testing methods that have been introduced, new tests in clinical cardiology, preferred imaging techniques, the impact of the Internet on diagnostic testing, and the growing direct-to-consumer movement in medical testing.

Product Details

ISBN-13: 9780816035304
Publisher: Facts on File, Incorporated
Publication date: 12/01/1997
Pages: 419
Product dimensions: 5.99(w) x 8.95(h) x 0.78(d)

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Chapter One


abdominal tap (belly tap, paracentesis, peritoneal fluid analysis) An invasive procedure in which a very long needle is inserted in the abdominal cavity to obtain fluid for either diagnostic or therapeutic purposes. The abdominal tap is a rapid way for clinicians in a hospital setting to distinguish a "surgical" abdomen (i.e., one requiring surgery) from a "nonsurgical" abdomen. Diagnostic paracentesis is performed to determine the cause of an increase in intraabdominal fluids. This is most commonly due to cirrhosis of the liver but is also caused by carcinoma, inflammation (peritonitis, pancreatitis, ruptured diverticulitis), and abdominal trauma with rupture of organs or blood vessels. One of the more important laboratory values obtained in the analysis of peritoneal fluid is the protein level, which is low in transudates (e.g., ascitic fluid) and high in exudates (e.g., inflammation and malignancy). The abdominal tap provides useful information in about 80% of cases; it may reveal unclotted blood, which indicates that bleeding is occurring within the abdomen; inflammatory cells, which suggests pancreatitis, appendicitis, diverticulitis, or rupture of an organ; or malignant cells, which may be the first indication of cancer.

  Patient preparation Before the procedure, patients may be given a tranquilizer.

Procedure The patient lies on his/her back and the abdomen is sterilized with appropriate cleansing solutions. The procedure consists of the insertion of a long, 20- or 18-gauge needle on either side of the navel,from which the physician obtains fluids for chemical analysis and a sample of cells to be examined under the microscope.

Specimen Peritoneal fluid.

Reference range Normally a few mesothelial cells may be seen in the fluid obtained from an abdominal tap.

Abnormal values Fresh blood and inflammatory or malignant cells may be seen as indicated above.

Cost $100-$200.

ACE See angiotensin-converting enzyme.

acetaminophen (Tylenol(r)) Acetaminophen is a drug used to relieve pain and reduce fever. It differs from aspirin in that it has little anti-inflammatory activity. Overdose can result in fatal liver failure, and serum levels of acetaminophen are usually requested by the patient's physician when an overdose is suspected.

Patient preparation No preparation is required, other than for drawing blood.

Procedure Acetaminophen is measured by immunoassay procedures, using either fluorescence polarization immunoassay (FPIA) or ELISA.

Specimen Serum, plasma, urine.

Reference rang Up to 25 [micro]g/ml is within the normal therapeutic range.

Abnormal values Toxicity occurs at levels of greater than 50 [micro]g/ml.

  Cost $25-$50.

acetone See urinalysis.

acetowhite lesion This lesion is a whitish patch on a woman's cervix that is seen by colposcopy when "painted" with Lugol solution (5% acetic acid, vinegar). White (the normal color of the cervix is pink) often indicates changes on the surface of the cervix that pathologists call hyperkeratosis and parakeratosis. These changes may be associated with cancer, precancerous changes known as cervical intraepithelial neoplasia (CIN, also called dysplasia), and infection by the human papillomavirus (HPV), which causes condyloma, a precancerous change.

Patient preparation The preparation is that for a colposcopy.

Procedure The woman lies on her back with her feet in stirrups while the gynecologist examines the cervix with a low-power microscope. The gynecologist coats the cervix with Lugol's solution, which stains the normal tissue a mahogany brown color, leaving the areas of potential disease (e.g., HPV infection, squamous metaplasia, dysplasia, and carcinoma) unstained. Whitish areas that suggest an abnormal lesion are biopsied, and the biopsy is submitted to a pathologist for evaluation.

Specimen Tissue sample, i.e., a biopsy.

Reference range No lesion, or mild inflammation.

Abnormal values HPV infection, metaplasia, dysplasia, and carcinoma.

  Cost See cervical intraepithelial neoplasia, colposcopy, HPV.

acetylcholine receptor antibodies A family of antibodies that develops in myasthenia gravis, a disease that affects the transmission of nerve impulses. In normal muscle, the chemical acetylcholine is released from nerve endings and binds to the molecules known as receptors, resulting in muscle contraction. In myasthenia gravis, antibodies act against the patient's own acetylcholine receptors. This occurs in up to 95% of patients with myasthenia gravis and prevents the binding of acetylcholine to the receptors, causing muscle weakness.

  Patient preparation No preparation is required, other than for drawing blood.

Procedure The antibodies are measured in the serum by a method known as radioimmunoassay.

Specimen Serum. Specimen must be kept at room temperature until analysis.

Reference range Negative, or less than 0.03 nmol/L.

Abnormal values Acetylcholine antibodies are found in myasthenia gravis.

Cost $75-$100.

Comments Failure to maintain the specimen at room temperature will interfere with results. Patients undergoing thymectomy, thoracic duct drainage, immunosuppressive therapy, or plasmapheresis may show reduced levels. Patients with amyotrophic lateral sclerosis may show false-positive results.

acetylcholinesterase See cholinesterase.

acetylsalicylic acid See aspirin.

acid-fast stain Acid-fast stain is a general term for any number of special stains used to identify Mycobacterium species, the most important of which is M. tuberculosis, the bacterium that causes tuberculosis. Acid-fastness is related to the composition of the bacterium's outer capsule. While acid-fastness is relatively specific for mycobacteria, it is also seen in some pollens, keratohyaline (a skin protein), lipofuscin (a product of cellular degradation), lead inclusions, and other microorganisms, including Nocardia, Histoplasma, and other bacteria. There are other, nontuberculous mycobacteria in the environment that stain with the acid-fast technique. In the appropriate setting, however, a positive acid-fast stain is usually regarded as evidence that the person has tuberculosis. Pulmonary tuberculosis is the most serious of the conditions caused by M. tuberculosis, which can be diagnosed either on a smear of sputum or on a biopsy of lesions of the lungs that are "suspicious" when the upper respiratory tract is examined by bronchoscopy. Other body sites can be evaluated by aspiration of fluids or by tissue biopsy.

Patient preparation Brush teeth or remove dentures and rinse mouth with water before obtaining a "deep cough" specimen. Saliva from the mouth is of little use. Tuberculosis from other body sites can be evaluated by aspirating fluids or by biopsy of tissues using standard aseptic procedures with local anesthesia.

Procedure Once the specimen is obtained from the patient, it is smeared on a glass slide which is dipped in a number of dyes to determine whether the organism is acid-fast or not. M. tuberculosis is slow to grow in culture; identification and determination of sensitivity to antibiotics may take four to six weeks.

Specimen Sputum.

Reference range No acid-fast staining.

Abnormal values Positive staining for acid-fast bacteria indicates the presence of Mycobacterium species. This finding must be followed up by a culture to determine the species and its sensitivity to antibiotics. A negative result must also be followed up by a culture since this test is of relatively low sensitivity.

Cost $50-$100.

Comments With the recent increase in tuberculosis and the prevalence of immunosuppressed individuals, particularly those with AIDS, newer techniques have been developed to speed the detection and identification of mycobacteria. The technique of polymerase chain reaction (PCR) may be used to detect early growth of M. tuberculosis. PCR shortens the time needed to identify mycobacteria to 24 hours, allowing early administration of antibiotics. A recent phenomenon of considerable concern to public health authorities is the emergence of mycobacteria that are resistant to the antibiotics formerly successful in treating tuberculosis.

acidified serum lysis test See Ham test.

acid infusion test See Bernstein test.

acid mucopolysaccharides This test is used in the diagnosis of mucopolysaccharidosis, a genetic deficiency in carbohydrate metabolism. An enzyme deficiency causes dermatan sulfate and heparin sulfate to accumulate in tissues. Its most severe form is Hurler's syndrome, also known as gargoylism, which has an early onset and commonly causes death by the age of ten.

Patient preparation No preparation is required, other than for obtaining urine.

Procedure This test is performed on a 24-hour urine specimen that is kept refrigerated and sent to the laboratory immediately after collection. See timed collection in Glossary.

Specimen Urine.

Reference range The normal values vary with age and are expressed as milligrams of glucuronic acid per gram of creatinine per 24 hours. At age two, this value is from 8 to 30, by early adolescence, it drops to between 0 and 12.

Abnormal values Values greater than 40 to 50 are suggestive of Hurler's syndrome.

Cost $35-$50 for the screening test.

Comments Improper specimen collection or handling will interfere with interpretation of results. Heparin therapy can cause elevated levels. False-positive levels occur in 5% of urine screening tests for acid mucopolysaccharides.

acid phosphatase Acid phosphatase is a group of enzymes present in the prostate gland, semen, liver, spleen, red blood cells, bone marrow, and platelets that can be separated and analyzed according to their source. Serum levels of acid phosphatase were formerly measured to diagnose and monitor the progress of prostate cancer. However, an increase in acid phosphatase also occurs in other conditions, thus necessitating newer tests to measure serum levels of PSA (prostatic specific antigen) and a test to measure acid phosphatase of prostatic origin.

Patient preparation Any manipulation of the prostate, such as massage, catheterization, or rectal examination should not be performed within 48 hours of obtaining the specimen.

Procedure The procedure consists of measuring the acid phosphatase in the serum by various laboratory methods.

Specimen Serum. When performed outside the hospital setting, the serum must be separated from the red blood cells and frozen before sending it to the laboratory.

Reference range Less than 3.0 mg/L.

Abnormal values Increased in: prostatic carcinoma, prostate infarction, Paget's disease, Gaucher's disease, multiple myeloma.

Cost $25-$45.

Comments This test is not specific for prostate cancer and, as previously indicated, has been largely superseded by other tests. Prostate manipulation and hemolysis cause falsely elevated results. Acid phosphatase levels drop abruptly if the specimen is not properly preserved. See prostate-specific antigen.

acquired immunodeficiency syndrome (AIDS) This disease has been linked with the human immunodeficiency virus (HIV), which invades specific cells in the immune system. This causes a decline in the body's ability to fight infection, resulting in secondary infections by microorganisms that do not normally cause disease. HIV infection may be present for as long as ten years before the symptoms of AIDS appear. Testing for HIV is strictly regulated by state and federal agencies because of the well-known social impact of HIV positivity. Information about HIV test results are kept confidential and may only be sent to nonphysicians with the written consent of the patient. Currently there are several types of tests used to detect and monitor HIV infection. Confide is a new product available through pharmacies. It is a home test; the blood samples are obtained from the finger and placed on a filter paper which is sent to the laboratory via mail. Patient confidentiality is maintained through the use of a 13-digit PIN number attached to the kit. Seven to ten days after mailing the sample, the patient is instructed to call the laboratory and give the assigned PIN number. The results are given to the caller along with the appropriate counseling. Another test, OraShure, is available through physicians and uses a sponge to obtain mucosal secretions from the mouth.

Screening tests These tests are known by the acronym ELISA (enzyme-linked immunosorbent assay) and detect antibodies to HIV that may be present in the patient's blood. Screening tests are used by blood banks to detect HIV-infected blood. Transfusion of an HIV-infected unit of blood virtually guarantees that the blood recipient will also become infected with HIV. Screening tests are also used to evaluate a person who may have been infected with HIV. Screening tests generally detect the anti-HIV antibodies approximately four to eight weeks after infection. Newer tests are being developed to detect the viral antigen, but they are not widely available or approved for clinical use. All screening tests that are positive are then retested by Western blot technique, which, while more reliable than the ELISA procedures, is more costly and difficult to perform.

Monitoring tests These tests monitor the course of AIDS and response to treatment. The p24 ELISA test measures HIV's p24 antigen, which for a time was used to indicate the progression of AIDS. Analysis of the T cell, a type of lymphocyte, is a more comprehensive test that measures the number of T cells in circulation. T cells are a type of white blood cell required for the "cell-mediated" arm of the immune response. The most commonly performed monitoring test for AIDS is the measurement of a subset of T cells, known as CD4 ("helper") T cells, and the ratio of the number of CD4 T cells to another subset of T cells known as CD8 ("suppressor") T cells. CD4 T cells help other cells of the immune system function in an optimal fashion and, in the healthy individual, are more abundant than the CD8 cells. As AIDS progresses, the number of all T cells decreases, especially the CD4 T cells. The number of B cells, the other major type of lymphocyte that is responsible for producing antibodies, usually remains normal throughout the course of AIDS.

New Tests A number of tests are being developed that are more sensitive, allowing earlier detection of HIV infection. Many of these tests are based on polymerase chain reaction (PCR) and are currently used to confirm the presence of HIV. As these tests become easier to perform and more cost efficient, they are likely to become more readily available for monitoring the effectiveness of treatment. These tests are primarily used to determine the number of viruses present in the circulation (viral load).

Patient preparation No preparation is required, other than for drawing blood.

Procedure ELISA is performed on serum. T cell analysis and viral load testing require whole blood specimens which are obtained within 24 hours of testing.

Specimen Serum for ELISA. Heparanized whole blood for T cell and viral load studies, which must be kept at room temperature prior to analysis.

Reference range

ELISA  Negative.
p24  Negative
PCR  Negative
T and B Cells Ratio of greater than 1.
CD4 CD8 ratio Ratio of greater than 1.
CD4 T cells Greater than 2000.
Western blot  Negative
HIV RNA Quantitation Negative

Abnormal values Positive findings in any of the above tests when confirmed by Western blot are diagnostic of HIV infection.

ELISA   $25-$50.
p24  $35-$55.
PCR  $100-$150.
T and B cells $75-$150.
CD4 CD8 ratio $75-$150.
CD4 T cells $75-$150.
Western blot   $35-$75.
HIV RNA Quantitation $200-$300.

Comments False-positive (i.e., reporting a person as positive for HIV who is actually negative) results for HIV testing are extremely unusual given the use of confirmatory tests, particularly the Western blot. False-negative (i.e., reporting a person as negative for HIV who is actually positive) results for HIV can occur during the "window period" interval (i.e., between the time a person is infected with HIV to the time enough anti-HIV antibodies are produced to be detected by the ELISA test).

ACTH See adrenocorticotropic hormone.

activated partial thromboplastin time (aPTT) The aPTT test is used in preoperative screening for increased bleeding tendencies and to monitor therapy with heparin and oral anticoagulants, drugs used to decrease clot formation. The aPTT test evaluates the time required for the clotting proteins or coagulation factors to form a fibrin clot.

Patient preparation No preparation is required, other than for drawing blood.

Procedure The procedure consists of mixing the patient's plasma with an "activator" and measuring the time required to form a clot.

Specimen Citrated plasma. The sample should be analyzed within two hours of being drawn from the patient, or the plasma should be separated from the red blood cells and frozen.

Reference range A fibrin clot forms 25 to 36 seconds after the addition of the "activator."

Abnormal values Increased in: coagulation factor deficiencies (factors V, VIII, IX, X, XI, XII), disseminated intravascular coagulation, Hodgkin's disease, hypofibrinogenemia, leukemia, liver cirrhosis, vitamin K deficiency, von Willebrand's disease, drugs (e.g., heparin, oral anticoagulants, aspirin).

Cost $10-$25.

Comments Sample handling is critical for obtaining correct results. If the venipuncture tube is not properly filled, falsely elevated values in the aPTT test will be obtained.

acute phase reactants (APR) Acute phase reactants are proteins that rise and fall with acute inflammation. These proteins migrate in specific regions of a slab of gelatin-like material that has been subjected to an electric current. These proteins include [[Alpha].sub.1]-antitrypsin, [[Alpha].sub.1]-acid glycoprotein, amyloid A and P, anti-thrombin III, C-reactive protein, C1-esterase inhibitor, C3 complement, ceruloplasmin, fibrinogen, haptoglobin, orosomucoid, plasminogen, and transferrin. Screening tests for acute phase reaction are nonspecific and include erythrocyte sedimentation rate (ESR), plasma viscosity, and zeta sedimentation rate.

  Patient preparation No preparation is required, other than for drawing blood.

Procedure The serum is analyzed by placing it on a special tube and measuring how quickly the red blood cells settle to the bottom, which is known as the erythrocyte sedimentation rate.

Specimen Whole blood.

Reference range The normal ESR is 0 to 20 millimeters/hour.

Abnormal values Increased in: pregnancy, acute and chronic inflammation, tuberculosis paraproteinemias (e.g., Waldenström's macroglobulinemia), rheumatoid arthritis. Decreased in: polycythemia, sickle cell anemia, hyperviscosity, low fibrinogen.

Comments The normal range of acute phase reactants increases with age, while the absolute rates of speed at which the blood settles decrease.

adenovirus Any of a family of viruses that cause noninfluenzal acute respiratory disease, pneumonia, epidemic keratoconjunctivitis, acute febrile pharyngitis, and acute hemorrhagic cystitis. The tests for adenovirus either measure antibodies to adenovirus or detect adenovirus antigens by immune (antigen-antibody) reactions. Both types of tests are known as serologic tests because they are performed on the serum. Adenoviruses can also be cultured, but because viral cultures are cumbersome and time-consuming, serologic methods are preferred by many laboratories. Asymptomatic infections (e.g., without flu symptoms) with adenoviruses are common and may make it difficult to interpret the serum levels of the immunoglobulin (antibody) response to infection. As a rule, immunoglobulin M (IgM), a specific antibody, increases when a person is first exposed to a particular microorganism. After the acute infection resolves, an immunoglobulin G (IgG) antibody to the virus is produced, which usually indicates protection against future infections by the causative virus.

Patient preparation For the serologic tests, no preparation is required, other than for drawing blood. There may be some discomfort associated with obtaining specimens from the throat or rectum.

Procedure The serologic procedure consists of measuring the levels of the IgG and IgM antibodies in the serum. To culture a virus, the specimen must be inoculated on one of several cell types, since viruses cannot grow outside of living cells. After a period of several days, the cells are examined by a microscope to detect specific changes caused by adenoviruses.

Specimen Serum for serologic diagnosis. Throat, rectal, and bladder specimens for culturing the virus.

Reference range The normal values for adenovirus antibodies are somewhat patient-specific, as each person differs in his or her ability to produce antibodies. In absence of adenovirus, the culture cells have no changes.

Abnormal values Patients infected with adenovirus usually demonstrate a four-fold increase in titers from the "acute" serum and the "convalescent" serum. Infected cells in culture demonstrate typical changes seen by microscopy.

Serology  $80-$100.
Viral culture $110-$150

ADH See antidiuretic hormone.

adrenal antibodies A general term for antibodies that are formed against components of the adrenal gland. These antibodies occur in 40% to 60% of patients with adrenal insufficiency (Addison's disease).

Patient preparation No preparation is required, other than for drawing blood.

Procedure These antibodies are identified by covering a test tissue (e.g., monkey adrenal gland) with the patient's serum. If adrenal antibodies are present, they can be detected by the technique of indirect immunofluorescence.

Specimen Serum.

Reference range None present.

Abnormal values Adrenal antibodies are found in: adrenal insufficiency (Addison's disease), idiopathic hypoparathyroidism.

Cost $75-$115.

adrenocorticotropic hormone (ACTH, corticotropin) ACTH is a hormone secreted by the anterior pituitary gland that signals the adrenal gland to release steroids (cortisol, androgens, and aldosterone), critical to the normal functioning of the body. ACTH levels in the serum vary during the course of the day, peaking in the morning between 6 and 8 a.m. and in the evening between 6 and 11 p.m. ACTH is not routinely measured because it degrades in the plasma and is not required to diagnose routinely encountered clinical conditions. However, in patients with Cushing's syndrome, ACTH measurement is extremely important because ACTH levels help determine where the lesion is located.

Patient preparation The patient's physical activity should be restricted for 10 to 12 hours prior to testing. Medications (particularly corticosteroids) that may interfere with ACTH testing should be withheld for 48 hours if possible. The patient should be placed on a low-carbohydrate diet for two days before testing.

Procedure The serum is analyzed by immunoassay.

Specimen Plasma, frozen within 15 minutes. For suspected adrenal hypofunction, the sample should be obtained from the patient between 6 and 8 a.m. To rule out Cushing's syndrome as a diagnostic consideration, the venipuncture must be performed between 6 and 11 p.m. The sample should be collected in a plastic test tube or a heparinized tube, packed in ice, and sent to the laboratory immediately.

Reference range ACTH levels less than 120 pg/ml.

Abnormal values Increased in: adrenal insufficiency (Addison's disease), congenital adrenal hyperplasia, Cushing's disease, ectopic ACTH-producing tumors, Nelson's syndrome. Decreased in: secondary adrenocortical insufficiency, adrenal carcinoma, adenoma.

Cost $50-$75.

Comments Because of ACTH's variability over the course of the day, its diagnostic significance and reliability are limited. Confirmation of increased or decreased ACTH levels may require ACTH suppression or stimulation testing to evaluate changes in the functional activity of the adrenal gland.

aerobic culture See bacterial culture.

AFP See alphafetoprotein.

airway resistance Airway resistance is the resistance to the flow of air in the upper airways, which is evaluated in pulmonary function tests. Airway resistance is the result of the natural recoil (resiliency) of the upper airway structures (the oral and nasal cavities, larynx, and the nonrespiratory portions of the lungs, including the trachea, bronchi, and bronchioles), through which the air passes on the way to the functional portion of the lungs, the alveoli. Airway resistance testing includes evaluation of airway responsiveness, provocation testing (e.g., bronchial challenge), evaluation of sites of airflow resistance or closures, and characterization of the type of lung disease.

Patient preparation The patient should avoid heavy meals three hours before the test. This is a non-invasive test which measures the pressure of breathing under various conditions.

Procedure Noseclips and a mouthpiece are placed on the patient, who is then seated inside a chamber known as a body plethysmograph. Once the chamber is sealed and the pressure reaches an equilibrium, the patient is told to pant lightly, which reflects the resistance to airflow.

Reference range 0.6-2.8 cm [H.sub.2]O/liters per second.

Abnormal values Increased in: asthma, chronic obstructive lung disease, smokers.

Cost $60-$80.

ALA See delta-aminolevulinic acid.

alanine aminotransferase ALT was formerly called serum glutamine pyruvic transaminase (SGPT), and many physicians continue to use the older name. Alanine aminotransferase is an enzyme found primarily in the liver, with lesser amounts present in the kidneys, heart, and muscles. Under normal conditions, the levels of ALT in the blood are low. When liver damage occurs, ALT is released into the bloodstream, usually before the more obvious clinical findings (e.g., jaundice) of liver damage occur. ALT levels are therefore useful to the physician, because increased ALT is an early indicator of liver damage. The analysis of this enzyme has been automated and is usually included as part of a panel of blood chemistry tests.

  Specimen Serum or heparinized plasma.

Reference range Men 10-32 units/L. Women 9-24 units/L. Children 2 times that of adults.

Abnormal values

Increased in: viral or drug-induced hepatitis, infectious mononucleosis, chronic hepatitis, intrahepatic cholestasis, cholecystitis, active cirrhosis acute myocardial infarction.

Cost $10-$20 when performed as a single test.

Comments The measurement of ALT alone has little diagnostic value and must be used in conjunction with other chemistry assays and clinical indicators.

albumin Albumin is the most abundant protein in blood circulation. It is needed to maintain the osmotic pressure within the blood vessels, without which fluids would leak out of the circulation. Albumin provides nutrition to tissues and binds to various molecules, such as hormones, vitamins, drugs, and enzymes, transporting them through the body. Albumin is synthesized in the liver and is extremely sensitive to liver damage. Hypoalbuminemia, the decrease in albumin, may be caused by liver damage, inadequate dietary intake of protein as occurs in malnutrition, and renal disease, in which albumin and other proteins are not retained by the kidneys. Dehydration causes an increase in albumin concentration, known as hyperalbuminemia.

Patient preparation Urine measurements require a 24-hour collection period. See timed collection.

Procedure Analysis of albumin is generally done as part of a larger chemistry profile on an automated analyzer.

Specimen Albumin can be measured in many body fluids, including serum, cerebrospinal fluid, and urine. Serum measurements of albumin are usually part of a multichannel chemical analysis of the blood, while albumin in cerebrospinal fluid and urine is measured singly.

Reference range

Serum, male 4.2-5.5 g/dL.
Serum, female 3.7-5.3 g/dl.
Urine  3.9-24.4 mg/24 hrs.
Cerebrospinal fluid  15-45 mg/dL

Abnormal values Increased in: dehydration. Decreased in: liver disease, chronic disease, neoplasia, thyroid disease, burns, heart failure.

Cost $8-$35 when performed as a single test.

Comments Decreased albumin in serum suggests liver disease. The "liver enzymes" (alanine aminotransferase and aspartate aminotransferase) must be evaluated in conjunction with albumin measurements, to confirm the presence of liver damage. The presence of albumin in urine generally signifies kidney disease.

alcohol The alcohol consumed in alcoholic beverages such as beer, wine, and liquors is ethyl alcohol (ethanol). After ethanol is consumed, it reaches a peak in the blood in about 30 minutes. Approximately three hours are needed to metabolize and eliminate each ounce of ethanol ingested. Blood alcohol measurements are fairly reliable for many hours after an individual ingests the last drink.

Patient preparation No preparation is required, other than for drawing blood or collecting urine. When blood samples are to be used, the venipuncture site must not be cleaned with alcohol pads because this would contaminate the specimen. The urine collection need not be a timed specimen.

Procedure Breath measurements are generally carried out by law enforcement officers, often at the site of a traffic violation where alcohol use is suspected. Alcohols are volatile substances; therefore it is important that the specimen container be kept tightly sealed until the time of analysis. Serum and urine ethanol are measured in the laboratory by immunoassay or gas-liquid chromatography; other alcohols are measured by gas-liquid chromatograpy.

Specimen Ethanol can be measured in the blood, breath, or urine.

Reference range Negative.

Abnormal values Greater than 0.05% (50 mg/dL) is considered toxic. Elevated levels of alcohols cause inebriation, liver, and brain damage.

Cost $25-$75. Higher costs are incurred when the test is used for legal purposes.

Comments Blood specimens are more accurate than urine when quantitative results are required. Proper specimen handling is extremely important for accurate results.

aldolase Aldolase is an enzyme that converts sugar to energy. Though most prominent in skeletal muscle, it is present in all tissues. Aldolase is elevated in the serum in skeletal muscle disease or injury and is less common in other conditions. It is measured when inflammatory disease of muscle (myopathy) is suspected. The intensity of the increase reflects the severity of the myopathy, and it can be measured serially to monitor the effect of corticosteroid therapy on the course of disease. Aldolase may also be elevated early in the clinical course of patients with muscular dystrophy.

  Patient preparation Patient should fast for eight hours prior to the test.

Procedure Aldolase is determined by the conversion of an uncolored substance to a colored substance that is measured by spectrophotometry.

Specimen Serum should be separated and frozen as quickly as possible.

Reference range 3.1-7.5 units/L.

Abnormal values Increased in: Duchenne's muscular dystrophy, dermatomyositis, polymyositis, trichinosis, metastatic carcinoma, myelocytic leukemia, megaloblastic anemia, hemolytic anemia, tissue death (infarction).

Cost $15-$25.

Comments Because aldolase is relatively nonspecific, it is not commonly requested by clinicians unless they are monitoring muscle diseases.

aldosterone Aldosterone is a hormone of the adrenal gland that helps control the electrolyte balance in the body by regulating the reabsorption of sodium and chloride in exchange for potassium and hydrogen ions in the kidneys. Aldosterone helps maintain blood pressure and blood volume. Secretion of aldosterone is controlled by the renin-angiotensin system which produces an enzyme, angiotensin II, that stimulates the synthesis and secretion of aldosterone. Secretion of aldosterone is also controlled by concentrations of potassium in the circulation. High serum potassium levels elicit secretion of aldosterone, while low concentrations of sodium cause the release of renin which stimulates aldosterone secretion. Aldosterone measurements are used increasingly in the study of hypertension.

Patient preparation The patient should be on a normal salt diet. Diuretics, antihypertensive drugs, oral contraceptives, estrogens, and licorice (which can cause hypertension) should be terminated two to four hours before testing. No recent radionuclide studies (scans) should be performed before drawing the specimen.

Procedure The patient must be at rest and lying down for the first venipuncture. Postural changes are evaluated by drawing another sample while the patient is up and about four hours after the initial specimen is collected. Aldosterone can also be measured in 24-hour urine samples. Measurements are made by RIA methods.

Specimen Serum, plasma, or urine. Specimens should be transported on ice and frozen as soon as possible after being obtained.

Reference range Plasma levels are less than 20 ng/dL in men, 30 ng/dL in non-pregnant women, 100 ng/dL in pregnant women, and 70 ng/dL in children. Urine levels are usually less than 50 [micro]g/24 hours.

Abnormal values Increased in: adrenocortical adenoma or carcinoma, bilateral adrenal hyperplasia, renovascular hypertension, liver disease, congestive heart failure, cirrhosis, nephrotic syndrome, pregnancy (3rd trimester). Decreased in: primary hypoaldosteronism, salt losing syndrome, toxemia of pregnancy.

Cost $180-$200.

Comments Failure to observe dietary restrictions or postural procedures interferes with the interpretation of test results. Aldosterone measurements are generally carried out together with potassium, sodium, and renin levels in the evaluation of hypertension and suspected lesions of the adrenal gland.

alkaline phosphatase ("alk phos") Alkaline phosphatase (ALP) is an enzyme normally present in the blood. Various subtypes known as isoenzymes are found in the liver, intestines, and bone cells. ALP is involved in bone calcification, and lipid and metabolite transportation. Conditions that stimulate bone cell activity cause elevated levels of alkaline phosphatase. The liver isoenzyme of ALP is elevated in biliary obstruction. Because an elevated total ALP level can indicate either liver or bone disease, additional studies must be carried out to determine the exact cause of the elevation. Since ALP concentrations rise during active bone formation in growth, infants, children, and adolescents normally have levels up to three times those of adults. Pregnancy can also cause an increase in ALP levels.

Patient preparation No preparation is required.

Procedure Alkaline phosphatase is measured by spectrophometry.

Specimen Serum.

Reference range Because reference ranges are dependent on the methodology used by the laboratory, these ranges can vary widely. In adult males, the range is 90-250 units/liter; in adult females, 80-200 units/liter.

Abnormal values Increased in: hepatobiliary disease (e.g., viral hepatitis, severe biliary obstruction, biliary cirrhosis, intrahepatic cholestasis), Paget's disease of bone, osteomalacia, osteogenic sarcoma, bone metastasis, hyperparathyroidism, infectious mononucleosis. Decreased in: hypophosphatasia, protein deficiency, magnesium deficiency.

Cost $20-$40 when performed as a single test.

Comments Because ALP exists in various tissues, the finding of elevated levels of total ALP must be followed by more specific testing such as ALP isoenzymes. Additional studies of bone or liver chemistries are used to determine the primary cause of elevations. ALP is generally part of a routine chemistry profile.

alkaline phosphatase isoenzymes Alkaline phosphatase is an enzyme with several subtypes known as isoenzymes, which are more common in certain organs. The isoenzymes of greatest clinical significance are those that occur in the liver, bone, intestine, and placenta. The intestinal isoenzyme occurs almost exclusively in individuals with blood group B or O and is markedly elevated eight hours after a fatty meal. The placental isoenzyme first appears in mid to late pregnancy, accounts for half of all alkaline phosphatase during the third trimester, and drops to normal levels after the woman delivers. Another, the Regan isoenzyme, resembles the placental isoenzyme of alkaline phosphatase and is present in some patients with cancer. A number of methods have been developed in the laboratory to separate the isoenzymes according to subtype. The primary use of this test is to determine which type of ALP isoenzyme is predominant when there is an elevation in total alkaline phosphatase.

  Patient preparation No preparation is required.

Procedure ALP isoenzymes can be measured by a variety of methods. The older methods involve heating or treating with urea. Currently, electrophoresis or isoelectric focusing are the methods of choice.

Specimen Serum.

Reference range

Liver   20-130 units/L.
Bone 20-120 units/L

Abnormal values An increase in the bone isoenzymes usually indicates Paget's disease of the bone. Bone isoenzymes are also increased in bone-forming tumors and in pregnancy.

Cost $50-$80.

Comments This test should not be performed if the total alkaline phosphatase levels are within the laboratory's reference (i.e., normal) range, because the results would have little clinical significance. These tests are only semiquantitative and are subject to significant variation. Other laboratory tests and clinical findings should be used in conjunction with alkaline phosphatase isoenzymes when making a diagnosis.


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