Lab Test Glossary L

Lactate dehydrogenase (ldh): Many different types of body cells contain the enzyme lactate dehydrogenase (LDH), particularly those in the heart, kidney, liver, and muscle. LDH levels may be abnormally high in heart attack (myocardial infarction) and liver disease, as well as other diseases. LDH plays an important role in energy production in cells. LDH levels are used for assessment of myocardial infarction, liver disease, pernicious and megaloblastic anemia, pulmonary embolus, malignancy, and muscular dystrophy.
Leishmania donovani IGM Antibody (l. donovani Ab): Leishmania donovani is an infectious parasite that causes visceral leishmaniasis, including kala-azar, also known as black fever. Leishmania parasites are transmitted by the bite of female Phlebotominae sandflies. It is rarely found in the U.S., but has been reported in the states bordering Mexico.
Leptin: Leptin, a protein hormone expressed primarily by fat cells, helps to control body weight through effects on appetite centers in the brain. Leptin acts on a receptor site of the hypothalamus to curb appetite and increase energy expenditure as body fat stores increase. Typically, overweight individuals have higher leptin levels. Conversely, lean individuals tend to have lower leptin levels. Leptin is also produced by cells lining the stomach and placenta. Although mutations in both the leptin and leptin receptor genes have been found in a small number of morbidly obese human subjects with abnormal eating behavior, the majority of obese persons do not show such mutations and have normal or elevated circulating leptin levels. Leptin levels are 40% higher in women than in men. Serum leptin levels are lowered by fasting and increased by inflammation.
Lipoprotein (A) [lp(A)]: Lipoprotein (a) [Lp(a)] blood levels are mostly determined by inherited genes. Elevated levels of Lp(a) are associated with an increased risk of coronary heart disease. Lp(a) is an atherogenic (plaque-producing) plasma protein whose structure resembles that of low-density lipoprotein (LDL). Lp(a) appears to competitively inhibit plasminogen activation, thus interfering with fibrinolysis, or the breakdown of blood clots, and thus increasing thrombogenic or clotting risk. Increased Lp(a) levels are associated with rapid progression of coronary disease and an increased risk of clinical recurrence after angioplasty. Lp(a) concentrations are not affected by diet, but can be lowered by some medications, such as Niacin.
Low Density Lipoprotein (ldl): Low density lipoproteins (LDL) are known as the “bad cholesterol” because they deliver cholesterol to the body. LDL is made by the liver under genetic control and also enters the body through cholesterol-containing foods (i.e., animal products). LDL deposits excess cholesterol in walls of blood vessels and contributes to the development of atherosclerosis. Thus, higher levels of LDL cholesterol are associated with an increased risk for coronary heart disease. Reduction of LDL cholesterol levels is associated with regression of heart disease.
Low Density Lipoprotein/High Density Lipoprotein Ratio (ldl/hdl ratio): The low density lipoprotein/high density lipoprotein (LDL/HDL) ratio is the ratio of “bad cholesterol” to “good cholesterol” and is used because a high level of HDL may partially offset the negative effects of a high LDL level. A ratio of 4.5 represents an average risk level, while people with ratios of 3 or less have only half the risk of heart disease as does the population at large. Evaluation of cardiac risk requires information about total cholesterol, triglycerides, LDL-cholesterol, HDL-cholesterol, and ratios of LDL- cholesterol or total cholesterol to HDL-cholesterol.
Luteinizing Hormone (LH): Luteinizing hormone (LH) is released by the pituitary gland. In women, a surge of LH in the middle of the menstrual cycle first causes ovulation, then stimulates the ovaries to produce estrogen and progesterone for about a week. LH then remains dominant in the luteal phase of the menstrual cycle in order to maintain the corpus luteum and endometrium in the event of pregnancy. In men, LH stimulates the production of androgen (a male hormone) by the testes. Increased levels of LH are associated with menopause, primary ovarian hypofunction, and polycystic ovarian syndrome in females, and primary hypogonadism in males. Decreased LH levels are associated with secondary and tertiary ovarian hypofunction in females and hypogonadism in males.
Lyme Disease IGM Antibody (borrelia burgdorferi IGM Antibody, b. burgdorferi Ab): Borrelia burgdorferi (B. burgdorferi) is the bacterium that causes Lyme disease. This disease may cause many different signs and symptoms including rash, arthritis, central nervous system problems, and heart-related ailments. The presence of the IgM antibody against B. burgdorferi indicates recent exposure to or infection with this bacterium. Transmission of B. burgdorferi is via the bite of an infected tick. In the majority of cases, it is easily treated and does not progress to the chronic stage.
Lymphocyte count: A lymphocyte is a type of white blood cell that identifies foreign substances, bacteria and viruses in the body and produces antibodies against them. Lymphocytes are the primary components of the immune system and play an important role in the body?s immune response. Lymphocytes are produced in the bone marrow and are divided into T-cell and B-cell lymphocytes. Lymphocytes increase in number in response to many types of viruses and with leukemia. A variety of diseases and conditions, including HIV infection, can decrease lymphocyte numbers. Corticosteroids and other immunosuppressive medications can also lower the lymphocyte count.
Lymphocyte Percentage: Lymphocytes, a type of white blood cell, make up 20 to 40% of all white blood cells in the bloodstream. Lymphocytes identify foreign substances, bacteria and viruses in the body and produce antibodies against them. Lymphocytes, produced in the bone marrow, are comprised of B-cell and T-cell lymphocytes. The lymphocyte percentage goes up in response to many types of viruses and with leukemia. A variety of diseases and conditions can decrease the lymphocyte percentage. Corticosteriods and other immunosuppressive medications can also cause reductions in lymphocytes.
Lymphotactin: Lymphotactin is a protein that chemically attracts the white blood cells called lymphocytes. Lymphotactin is produced by activated progenitor T-cells. Lymphotactin has been linked to autoimmune diseases and to the rejection of transplanted organs.
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