Definition Lysergic acid diethylamide (LSD), also known as "acid," belongs to a class of drugs known as hallucinogens, which distort perceptions of reality. LSD is the most potent mood- and perception-altering drug known: doses as small as 30 micrograms can produce effects lasting six to 12 hours. Purpose In the United States, LSD has no accepted medical use and its manufacture is illegal. Description LSD...

Definition Lymphogranuloma venereum (LGV) is a sexually transmitted systemic disease (STD) caused by a parasitic organism closely related to certain types of bacteria. It affects the lymph nodes and rectal area, as well as the genitals, in humans. The name comes from two Latin words that mean a swelling of granulation tissue in the lymph nodes resulting from sexual intercourse. Granulation tissue is...

Definition Lymphocytopenia is a condition marked by an abnormally low level of lymphocytes in the blood. Lymphocytes are a specific type of white blood cell with important functions in the immune system. Description Lymphocytes normally account for 15-40% of all white cells in the bloodstream. They help to protect the body from infections caused by viruses or fungi. They also coordinate the activities of...

Definition Lymphocytic choriomeningitis (LCM) is a viral infection of the membranes surrounding the brain and spinal cord and of the cerebrospinal fluid. Description Lymphocytic choriomeningitis virus infection is relatively rare and recovery usually occurs spontaneously within a couple of weeks. Many cases are probably not even identified because the symptoms range from extremely mild to...

Definition Lymphocyte typing focuses on identifying the numbers and relative percentages of lymphocytes in an individual's bloodstream. Lymphocytes, primarily T cells and B cells, are types of white blood cells, the underlying supports of the immune system in the bloodstream. Purpose Determining the numbers and relative percentages of T cells and B cells provides information on the state of a person's...

Description Lymphedema involves blockage of the lymph vessels, with a resulting accumulation of lymphatic fluid in the interstitial tissues of the body. The lymphatic system consists of lymph vessels and lymph nodes throughout the body. The lymph vessels collect lymphatic fluid, which consists of protein, water, fats, and wastes from cells. The lymph vessels transport the fluid to the lymph nodes, where...

Definition Lymphangiography is a type of diagnostic testing technique in which x rays (called lymph node angiograms) and the injection of a contrast medium (a substance that provides a contrast between the tissue or organ being filmed and the medium) are used to visualize lymphatic circulation and the lymph nodes. Purpose The lymphatic system consists of tissues, organs, and vessels that aid in circulating...

  Definition Lymphadenitis is the inflammation of a lymph node. It is often a complication of a bacterial infection of a wound, although it can also be caused by viruses or other disease agents. Lymphadenitis may be either generalized, involving a number of lymph nodes; or limited to a few nodes in the area of a localized infection. Lymphadenitis is sometimes accompanied by lymphangitis,...

Definition A lymph node biopsy is a procedure in which all or part of a lymph node is removed and examined to determine if there is cancer within the node. Purpose The lymph system is the body's primary defense against infection. It consists of the spleen, tonsils, thymus, lymph nodes, lymph vessels, and the clear, slightly yellow fluid...

Definition Lyme disease is an inflammatory disease transmitted through the bite of a deer tick carrying the spiral-shaped bacterium Borrelia burgdorferi. Symptoms can include skin rash, joint inflammation,fever , headache , fatigue, and muscle pain . Lyme disease is also called Lyme borreliosis. Description Lyme disease is an...

Definition The luteinizing hormone (LH) test is a test of the blood or urine to measure the level of luteinizing hormone (lutropin). This hormone level is highest immediately before a woman ovulates during her menstrual cycle. Purpose The LH test is frequently used to determine the timing of ovulation. Couples who are trying to become pregnant...

Definition Lung transplantation involves removal of one or both diseased lungs from a patient and the replacement of the lungs with healthy organs from a donor. Lung transplantation may refer to single, double, or even heart-lung transplantation. Purpose The purpose of lung transplantation is to replace a lung that no longer functions, or is cancerous, with a healthy lung. In...

Definition Lung surgery includes a variety of procedures used to diagnose or treat diseases of the lungs. Biopsies are performed to extract a small amount of tissue for diagnosis, resections remove a portion of lung tissue, and other surgeries are aimed at reducing the volume of the lungs, removing cancerous tumors, or improving lung function. Purpose The type of lung surgery performed...

Definition A lung perfusion scan and ventilation study are two diagnostic imaging studies. A lung perfusion scan assesses blood flow to the lungs. A lung ventilation study reveals the distribution of air space within the lungs. These are two separate studies that are often performed sequentially. The tests are called by different...

Definition Lung diseases due to gas or chemical exposure are conditions that can be acquired from indoor and outdoor air pollution and from ingesting tobacco smoke. Description The lungs are susceptible to many airborne poisons and irritants. Mucus present in the airways blocks foreign particles of a certain size, however it is unable to filter all airborne particulates....

Definition Small cell lung cancer is a disease in which the cells of the lung tissues grow uncontrollably and form tumors.   Description Lung cancer is divided into two main types: small cell and non-small cell. Small cell lung cancer is the least common of the two, accounting for only about 20% of all lung cancers. In the past, the disease was called oat cell cancer because, when viewed under a microscope,...

Definition Non-small cell lung cancer (NSCLC) is a disease in which the cells of the lung tissues grow uncontrollably and form tumors. Description There are two kinds of lung cancers, primary and secondary. Primary lung cancer starts in the lung itself, and is divided into small cell lung cancer and non-small cell lung cancer....

Definition Lung biopsy is a procedure for obtaining a small sample of lung tissue for examination. The tissue is usually examined under a microscope, and may be sent to a microbiological laboratory for culture. Microscopic examination is performed by a pathologist.  Purpose A lung biopsy is usually performed to determine the cause of abnormalities, such as nodules that...

Definition Lung abscess is an acute or chronic infection of the lung, marked by a localized collection of pus, inflammation, and destruction of tissue. Description Lung abscess is the end result of a number of different disease processes ranging from fungal and bacterial infections to cancer. It can affect anyone at any age. Patients who are most vulnerable include those weakened...

Definition A lumpectomy is a type of surgery for breast cancer . It is considered "breast-conserving" surgery because in a lumpectomy, only the malignant tumor and a surrounding margin of normal breast tissue are removed. Lymph nodes in the armpit (axilla) may also be removed. This procedure is called lymph node dissection . Purpose Lumpectomy is a surgical treatment...

Definition Lower esophageal ring is a condition in which there is a ring of tissue inside the lower part of the esophagus (the tube connecting the throat with the stomach). This tissue causes narrowing and partial blockage of the esophagus. Lower esophageal ring can also refer to the ring itself. Description Lower esophageal ring (also called Schatzki's ring and B-ring) affects...

Definition Low back pain is a common musculoskeletal symptom that may be either acute or chronic. It may be caused by a variety of diseases and disorders that affect the lumbar spine. Low back pain is often accompanied by sciatica, which is pain that involves the sciatic nerve and is felt in the lower back, the buttocks, and the backs of the thighs. Description Low...

Definition Liver transplantation is a surgery that removes a diseased liver and replaces it with a healthy donor liver.  Purpose A liver transplant is needed when the liver's function is reduced to the point that the life of the patient is threatened.  Demographics Compared to whites, those with African-American, Asian, Pacific Islander,...

Definition A liver scan is a diagnostic procedure to evaluate the liver for suspected disease. A radioactive substance which concentrates in the liver is injected intravenously and the image of its distribution in the body is analyzed to diagnose certain abnormalities. Purpose In the past, liver scans were used to evaluate the liver in a wide variety of...

Definition Liver function tests, or LFTs, include tests that are routinely measured in all clinical laboratories. LFTs include bilirubin, a compound formed by the breakdown of hemoglobin; ammonia, a breakdown product of protein that is normally converted into urea by the liver before being excreted by the kidneys; proteins that are made by the liver including total protein,...

Definition Liver encephalopathy is a potentially life-threatening disease in which toxic substances accumulate in the blood. Also known as hepatic encephalopathy or hepatic coma, this condition can cause confusion, disorientation, abnormal neurological signs, loss of consciousness, and death. Description A normally functioning liver metabolizes and detoxifies substances...

Definition Liver disease is a general term for any damage that reduces the functioning of the liver. Description The liver is a large, solid organ located in the upper right-hand side of the abdomen. Most of the liver lies under the rib cage, which helps protect it from physical injury. The liver is made up of two main lobes and two minor...

Definition Liver cancer is a relatively rare form of cancer but has a high mortality rate. Liver cancers can be classified into two types. They are either primary, when the cancer starts in the liver itself, or metastatic, when the cancer has spread to the liver from some other part of the body. Description Primary liver cancer Primary liver cancer is a relatively rare disease...

Definition A liver biopsy is a medical procedure performed to obtain a small piece of liver tissue for diagnostic testing. The sample is examined under a microscope by a doctor who specializes in the effects of disease on body tissues (a pathologist) to detect abnormalities of the liver. Liver biopsies are sometimes called percutaneous liver biopsies,...

Definition Lithotripsy is a therapeutic medical procedure used to disintegrate stones (calculi) in the urinary tract and kidneys. Extracorporeal shock wave lithotripsy (ESWL) uses shock waves generated outside the body and is noninvasive. Intracorporeal shock wave lithotripsy (ISWL) delivers shock waves through a specially designed scope used for the urinary tract (ureteroscope)...

Definition Listeriosis is an illness caused by the bacterium Listeria monocytogenes that is acquired by eating contaminated food. The organism can spread to the blood stream and central nervous system. During pregnancy, listeriosis often causes miscarriage or stillbirth. Description Listeriosis is caused by an infection with the bacterium Listeria monocytogenes....

Definition Liposuction, also known as lipoplasty or suction-assisted lipectomy, is cosmetic surgeryperformed to remove unwanted deposits of fat from under the skin. The surgeon sculpts and re-contours a person's body by removing excess fat deposits that have been resistant to reduction by diet or exercise . The fat is permanently...

Definition Lipids are water insoluble molecules and must be transported in the plasma as macromolecular complexes containing protein called lipoproteins. The lipoproteins are large aggregates (micelles) composed of cholesterol, triglycerides, phospholipids, proteins, and small amounts of carbohydrates. Generally, the core of the lipoprotein contains hydrophobic lipids surrounded...

Definition Lipidoses are genetic disorders, passed from parents to their children, characterized by defects of the digestive system that impair the way the body uses dietary fat. When the body is unable to properly digest fats, lipids accumulate in body tissues in abnormal amounts. Description The digestion, storage, and use of fats (lipids) from foods are complex processes that involve hundreds of chemical...

Definition The lipase test is a blood test performed to determine the serum level of a specific protein (enzyme) involved in digestion. Lipase is an enzyme produced by the pancreas, which is a large gland situated near the stomach. Lipase works to break down a certain type of blood lipid (triglycerides) into fatty acids. Lipase appears in the blood together with...

Definition Life support refers to a spectrum of techniques used to maintain life after the failure of one or more vital organs. Purpose A patient requires life support when one or more vital organs fail, due to causes such as trauma, infection, cancer, heart attack, or chronic disease. Among the purposes of life support are...

Definition Lichen simplex chronicus is a chronic inflammation of the skin (dermatitis ) characterized by small, round itchy spots that thicken and become leathery as a result of scratching. Description Also termed neurodermatis, lichen simplex chronicus is the result of chronic skin irritation. It occurs in 4-5 out of every thousand people. Initial irritation causes itching, and...

Definition Lichen planus is a skin condition of unknown origin that produces small, shiny, flat-topped,itchy pink or purple raised spots on the wrists, forearms or lower legs, especially in middle-aged patients. Description Lichen planus affects between 1-2% of the population, most of whom are middle-aged women. The condition is less common in the very young and the very old. The lesions are...

Definition A lice infestation, or pediculosis, is caused by parasites living on human skin. Lice are tiny, wingless insects with sucking mouthparts that feed on human blood and lay eggs on body hair or in clothing. Lice bites can cause intense itching . Description There are three related species of human lice that live on different parts of the body: ·        ...

Definition Leukotriene inhibitors are prescription medications that treat asthma and some allergies by blocking the formation or activity of leukotrienes—small mediator chemicals produced by cells in the body. Purpose More than 50 million Americans suffer from asthma and allergies. Asthma is one of the most prevalent chronic diseases in the United States, affecting 9 million...

Definition Leukocytosis is a condition characterized by an elevated number of white cells in the blood. Description Leukocytosis is a condition that affects all types of white blood cells. Other illnesses, such as neutrophilia, lymphocytosis, and granulocytosis, target specific types of white blood cells. Normal white blood cell counts are 4,300-10,800 white blood cells per microliter. Leukocyte or...

Definition Chronic leukemia is a disease in which abnormal, cancerous white blood cells are made in the bone marrow. Depending on the type of white blood cell that is involved, chronic leukemia can be classified as chronic lymphocytic leukemia or chronic myeloid leukemia. Description Chronic leukemia is a cancer that starts in the blood cells made in the bone...

Definition Leukemia is a cancer that starts in the organs that make blood, namely the bone marrow and the lymph system. Depending on their characteristics, leukemias can be divided into two broad types. Acute leukemias are the rapidly progressing leukemias, while the chronic leukemias progress more slowly. The vast majority of the childhood leukemias are of the acute form. Description The...

Definition Leukemia stains are laboratory tests done on bone marrow or blood samples to help diagnose specific types of leukemia. Purpose Leukemia stains are done to diagnose and classify leukemia. Blood contains red cells, several varieties of white cells, and platelets. Cancerous overproduction of any one type of cell produces one of many types of leukemia. A patient's...

Definition Lesch-Nyhan syndrome is a rare genetic disorder that affects males. Males with this syndrome develop physical handicaps, mental retardation, and kidney problems. It is caused by a total absence of an enzyme. Self injury is a classic feature of this genetic disease. Description Lesch-Nyhan syndrome was first described in 1964 by Dr. Michael Lesch and Dr. William Nyhan. The syndrome is...

Definition Leptospirosis is a febrile disease (fever ) caused by infection with the bacterium Leptospirainterrogans. L. interrogans is sometimes classified as a spirochete because it has a spiral shape. The disease can range from very mild and symptomless to a more serious, even life threatening form, that may be associated with...

Leprosy, also called Hansen’s disease, is responsible for active disease or disability in about four million people worldwide. Caused by an unusual bacterium called Mycobacterium leprae, leprosy primarily affects humans. Leprosy is found in tropical areas, such as Africa, South and Southeast Asia, and Central and South America. In the United States, cases of leprosy have been...

Definition Leishmaniasis refers to several different illnesses caused by infection with an organismcalled a protozoan. Description Protozoa are considered to be the most simple organisms in the animal kingdom. They are all single-celled. The types of protozoa that cause leishmaniasis are carried by the blood-sucking sand fly. The sandfly is...

Legionnaire disease is a type of pneumonia caused by Legionella bacteria. The bacterial species responsible for Legionnaire disease is L. pneumophila. Major symptoms include fever, chills, muscle aches, and a cough that is initially nonproductive. Definitive diagnosis relies on specific laboratory tests for the bacteria, bacterial antigens, or antibodies produced by the body’s...

Definition Leeches are bloodsucking worms with segmented bodies. They belong to the same large classification of worms as earthworms and certain oceanic worms. Leeches can primarily be found in freshwater lakes, ponds, or rivers. They range in size from 0.2 in (5 mm) to nearly 18 in (45 cm) and have two characteristic suckers located at either end of their bodies. Leeches consume the blood...