Glossary of Terms - h

Index

Click on a letter to jump to another subsection or click on "all" for the entire document.

a b c d e f g h i k l m n o p q r s t u v w all

Terms

Hashimoto's Thyroiditis: An autoimmune destructive disease characterized by atrophy of the thyroid gland.
HDL cholesterol: See high density lipoprotein cholesterol.
Hemoglobin: The oxygen-carrying pigment of red blood cells, it is manufactured in bone marrow, and composed of iron-containing heme and the protein globin. Many types of hemoglobin have been identified, however adult (A) and fetal (F) types are considered to be normal. Tests to measure hemoglobin concentration and to determine abnormal hemoglobin types are performed to identify anemias and other blood diseases.
Hemolysis: When the red blood cells break apart. Hemolysis can cause interference for certain assays.
Hepatitis: Inflammation of the liver, usually caused by bacterial or viral infection, drugs (including alcohol), toxins, or parasites. This disease is characterized by an enlarged liver, jaundice, diminished appetite, nausea, and abdominal pain. There are at least three forms of viral hepatitis (hepatitis A, hepatitis B, and non-A, non-B hepatitis). Hepatitis A, also known as infectious hepatitis, is transmitted by contaminated food or water and personal contact, and is most often found in children or young adults. Hepatitis B, formerly called serum hepatitis, may be transmitted through contaminated blood or needles, as well as sexually, and has a longer incubation period than that of hepatitis A. Hepatitis B can result in chronic active hepatitis. Non-A, non-B hepatitis is also transmitted through blood and can cause severe liver damage. Radioimmunoassays and enzyme-linked immunosorbent assays may be used to screen for hepatitis.
Hepatitis B surface antigen (HBsAg): A part of the hepatitis B virus that, when in the blood, is one of the earliest markers of infection with hepatitis B virus, appearing even before symptoms. Also found in blood of a carrier. HBsAg is tested for in the differential diagnosis of hepatitis.
Hepatoma: A malignant tumor of the liver (primary hepatocellular carcinoma) sometimes associated with hepatitis or cirrhosis. Elevated blood levels of alpha-fetoprotein (AFP) may indicate the presence of a hepatoma. AFP levels are useful in monitoring chemotherapeutic success in treating this condition.
High density lipoprotein cholesterol (HDLC): The fraction of plasma lipoprotein cholesterol component with most density (relative weight). It is thought to affect blood cholesterol levels by removing it from plasma and tissues and carrying it back to the liver for excretion after being acted on by bile. High levels of HDLC are considered to place an individual at a lower risk for coronary heart disease (atherosclerosis). Low levels of HDLC are associated with an increased risk for the disease. The density may be established by ultracentrifugation or electrophoresis.
Histogram: A graphic means of comparing magnitudes of frequencies or numbers of items; usually shown in bar graphs or columns.
Homocysteine: Homocysteine is an amino acid derived from the digestion of protein-rich foods.
Hormone: Chemical substances secreted by organs or parts of the body, especially the endocrine glands, into the bloodstream. Each hormone has a specific regulatory or functional effect.
Human Immunodeficiency Virus (HIV): Human Immunodeficiency Virus
Hydrolysis: A chemical reaction in which a compound reacts with water, resulting in its decomposition or alteration.
Hyperglycemia (high blood sugar): A condition in which the blood contains an abnormally high level of glucose, characteristic of diabetes mellitus.
Hyperthyroidism: A condition characterized by accelerated metabolism caused by an excessive amount of thyroid hormones (overactive thyroid).
Hypoglycemia (low blood sugar): A condition in which there is an abnormally diminished concentration of glucose in the blood, which may lead to convulsions or coma.
Hypothalamus: An area of the brain that regulates endocrine activity as well as somatic functions e.g.body temperature, sleep, appetite. Hypothalamic neurohormones (e.g.TRH) control various functions of the pituitary gland.
Hypothyroidism: A condition characterized by deficient production of thyroid hormones (underactive thyroid).