Glossary of Terms - a

Index

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Terms

Accuracy: The agreement of the test result with the true value of the sample.
ACD: A solution of acid, citrate, and dextrose used as an anticoagulant and preservative in storing blood for transfusions.
Acetaminophen: A pain reliever and fever reducer; the active ingredient in many medications. An overdose may be toxic.
Acetic acid: The acid found in vinegar, often used as a reagent: also used in the preparation of pharmaceuticals, and in industry.
Acetylcholinesterase (AChE): An enzyme present in various tissues, including muscle and red cells, that breaks down acetylcholine (a chemical released by nerves that activates muscle contractions) and helps to maintain proper transmission of impulses between nerve cells and between nerve cells and muscles; also called true cholinesterase. Measuring acetylcholinesterase in amniotic fluid may help confirm a suspected neural tube defect in the fetus.
Acetylsalicylic acid (ASA): Aspirin; salicylate. A pain reliever and fever reducer. See salicylates. An overdose can be toxic.
Acid phosphatase (Acid phos): An enzyme found primarily in the prostate and semen. Increased blood serum levels may indicate cancer of the prostate or may follow prostatic massage.
Acidosis: A condition marked by an accumulation of acids in body tissues and blood that may result from prolonged diarrhea or disorders such as diabetes and kidney disease, when not under control. Urine tests screen for acidosis. Determination of blood pH provides more accuracy.
Acquired immunodeficiency syndrome: See AIDS.
Ad: Symbol for a dichromatic absorbance. It is equal to the absorbance at the secondary wavelength subtracted from the absorbance at the primary wavelength.
Adrenal glands: Located near the kidneys, the adrenal glands produce a small amount of the male hormone, testosterone.
Agar: A medium used to grow microorganisms.
AIDS: Acquired immunodeficiency syndrome. A condition in which the normal immune system becomes depressed, rendering the affected individual unable to fight a number of serious and fatal infections. Human T-cell leukemia/lymphoma virus (HTLV-III) is associated with AIDS. The virus has been renamed human immunodeficiency virus (HIV). The presence of HIV antigen in the blood will confirm that an individual is infected with the virus and has AIDS. The presence of HIV antibody in the blood confirms that an individual has been infected with the AIDS virus. See antigen and antibody.
AIDS-related complex: See ARC.
Albumin: The most abundant protein component of blood, Produced primarily in the liver, albumin helps to keep the fluid portion of blood within the vessels, and helps transport drugs and other substances by way of the bloodstream. Low levels of albumin in the blood or its presence in urine may signal edema (the accumulation of fluid) as in pedal edema (in the ankles) or pulmonary edema (in the lungs), which may be symptoms of congestive heart failure, kidney or liver disease.
Alkaline phosphatase (Alk phos): An enzyme found mainly in liver and bone. Blood serum alkaline phosphatase is usually measured to detect liver or bone disease.
Alkalosis: A condition in which the blood and tissues contain an abnormally high level of alkali (usually too much bicarbonate), often caused by prolonged vomiting or hyperventilation. Symptoms include dizziness and jerky muscular contractions. Alkalosis can be detected in a urine test. Determination of blood pH provides more accuracy.
Alpha-fetoprotein (AFP): A substance produced by the fetus that is found in fetal serum, amniotic fluid, and the mother's bloodstream. Elevated levels of AFP may indicate that the baby has a neural tube defect such as spina bifida (incomplete closure of the spinal column) which can lead to paralysis of the lower limbs, repeated urinary tract infections, mental retardation or hydrocephalus ("water on the brain"). It is also a useful nonspecific tumor-associated antigen (tumor marker).
Alzheimer's disease: A disorder marked by progressive mental deterioration (dementia), including memory loss, confusion, reduction of functional activity, and fluctuations in alertness, usually beginning in later middle life. Use of dexamethasone suppression test (DST) has been suggested to help in differential diagnosis of dementia and depression (also a frequent disease of later life). This is important, as adequate treatment may produce improvement in depressive disease. See dexamethasone suppression test.
Aminoglycosides: A class of antibiotics specific for gram negative bacteria.
Amniocentesis: A prenatal diagnostic procedure in which a needle is inserted through the mother's abdomen into the uterus and amniotic sac to remove a sample of amniotic fluid. The fluid, containing fetal cells, proteins, and other substances, may be analyzed to detect genetic disorders, including Down syndrome (mongolism). An elevated level of AFP can indicate neural tube defects. See neural tube defect.
Amniography: A prenatal diagnostic procedure in which X-ray of the mother's uterus, after injection of a radiopaque substance, allows visualization of the fetus, the placenta, and the uterine lining. This may be used to confirm a diagnosis of neural tube defects.
Amniotic fluid: The fluid surrounding the developing fetus that is found within the amniotic sac contained in the mother's womb.
Amphetamine: A compound (or its derivatives) that acts as a central nervous system stimulant. Used as a stimulant in depressed states, to reduce appetite, and in attention-deficit disorders, it can also alleviate nasal congestion. Amphetamine use can lead to dependence. It has a high potential for abuse. Blood and urine tests can detect amphetamine use and toxic levels.
Amplicon: The product of PCR or LCR; a piece of DNA that has been synthesized using amplification techniques.
Amylase: A digestive enzyme produced largely by the pancreas and salivary glands that converts starches to sugars. Abnormally high levels of amylase in the blood or urine may be found in patients with inflammation of the pancreas or salivary glands (mumps).
Analyte: A substance that is undergoing analysis or is being measured.
Anemia: Below normal levels of red blood cells or hemoglobin, or both, which can be caused by many different conditions, including iron deficiency. Symptoms may include fatigue, weakness, headache, and dizziness. Appropriate blood tests will confirm the diagnosis of anemia and shed light on its etiology.
Anencephaly: Abnormal development of the brain in the fetus accompanied by absence of the bones of the cranial vault. Children born with this severe disorder die shortly after birth. Measurement of maternal blood and amniotic fluid levels of alpha-fetoprotein (AFP) can help diagnose this condition and other neural tube defects. See alpha-fetoprotein.
Antiarrhythmic: Any one of a group of drugs which prevent or control irregularities in the heart beat.
Antiasthmatic: Any one of a group of drugs which prevent or control spasms and narrowing of the lung's bronchi and bronchioles.
Antibiotics: Any substance derived from fungi or bacteria that destroys or inhibits the growth of microorganisms.
Antibody (Ab): A substance produced by the body in response to an antigen that specifically reacts with the antigen to destroy, inhibit, or neutralize it. The body produces antibodies as a defense against foreign substances. Antibodies may be identified and measured to determine whether an individual has been infected by a pathogen.
Antibody assays: Tests to determine levels of specific antibodies in the blood.
Anticoagulant: A chemical used to prevent blood clotting. Examples: EDTA, heparin, sodium citrate, sodium oxalate.
Anticonvulsant: Any of a group of drugs that prevent seizures or control their incidence or severity.
Antigen (Ag): Any substance that when introduced into the body (such as the protein coat of an invading pathogen) causes the formation of antibodies. Ag is also found on tissue and blood cells, and in body fluids. Measurement of antigen can help determine whether a particular disease will become active.
ARC: AIDS-related complex. A condition in which antibody tests for AIDS virus are positive and patients may exhibit enlarged lymph nodes, fatigue, fever, night sweats, weight loss, and unexplained diarrhea, but do not have any of the more serious complications of AIDS.
Arteriogram: X-ray visualization of the arterial lining after injection of radiopaque dye into a specific artery or into the bloodstream. It aids in the diagnosis of vascular occlusions and of athrosclerotic plaques, as well as of other cardiovascular abnormalities.
Assay: Analysis of a substance, or of components in a mixture, or of the biological, chemical, or pharmacological potency of a drug. Forms of assay include: Endpoint assay — a single measurement is made at a fixed time. Kinetic assay — increasing amounts of a product are formed with time, and are monitored at multiple points. Microbiological assay — measurement of the concentration of antimicrobials in biological material. Immunological assay — analysis or measurement is based on antigen-antibody reactions.
Assay (immunological): There are many types of immunological assays, including agglutination, complement-fixation, precipitation, immunodiffusion, and electrophoretic assays. Each type of assay utilizes either a particular type of antibody or a specific support medium (such as a gel) to determine the amount of antigen present.
Assay (Indicator-labeled immunoassays): Indicators are attached to the antigen or to the antibody to demonstrate that the antigen-antibody reaction has occurred. These assays have enabled measurement of many substances not previously measurable. Among these assays are: Enzyme immunoassay (EIA), Enzyme-linked immunosorbent assay (ELISA), Enzyme-multiplied immunoassay technique (EMIT), Fluorescence immunoassay (FIA), Fluorescence polarization immunoassay (FPIA) andRadioimmunoassay (RIA).
Attenuation: A decrease in light due to absorption by a chromagen in radiative energy attenuation technologies.
Autoimmune(autoimmunity): A condition characterized by a specific humoral or cell-mediated immune response against constituents of the body's own tissues.