Medical terms A–Z

A substance produced by certain white blood cells in reaction to contact with the human immunodeficiency virus (HIV).

Infected with the human immunodeficiency virus (HIV), the cause of acquired immunodeficiency syndrome (AIDS).

Welts that move: individual patches fade within a day while new ones rise elsewhere, which is what separates them from most other rashes.

The body's identity badge, read by T cells to tell its own healthy cells from infected, faulty or transplanted ones.

Hemophagocytic lymphohistiocytosis, abbreviated HLH, is a rare condition of excessive immune activation that damages organs and destroys blood cells.

A substance being studied in the treatment of multiple myeloma and several other types of cancer.

A rare inherited disorder that increases the risk of developing benign (not cancer) tumors of the skin and the uterus (leiomyomas) and malignant (cancer) tumors of the uterus (leiomyosarcoma) and…

A substance that blocks an enzyme needed by the body to make cholesterol and lowers the amount of cholesterol in the blood.

A protein that binds to the DNA and certain proteins in chromosomes.

A substance being studied in the treatment of several types of cancer.

The inherited cancer syndrome named for the polyps it does not produce, now generally called Lynch syndrome for exactly that reason.

The older name for a lymphoma that stands apart from every other one, in the cell that defines it and in the way it spreads.

Painless swelling of a node in the neck is the usual opening, sometimes with drenching night sweats and a fever that comes and goes.

A plant whose leaves, stems, and flowers have been used in some cultures to treat certain medical problems.

A system of remedies prepared by repeated dilution, based on principles that predate modern chemistry and conflict with it.

Homeopathy is an alternative medicine system based on treating symptoms with extremely diluted substances chosen to mimic those same symptoms.

The maintenance of stable internal conditions within a living system.

Homeostatic describes processes and mechanisms that maintain the body's internal stability despite ongoing changes in its external or internal environment.

An anticancer drug that belongs to the plant alkaloid family of drugs.

Receptors, not the messenger, decide the effect, which is why a single hormone can quicken the heart and slow the gut at once.

A cell protein that binds a specific hormone.

A test to measure the amount of certain proteins, called hormone receptors, in cancer tissue.

Hormones (estrogen, progesterone, or both) given to women after menopause to replace the hormones no longer produced by the ovaries.

In oncology, describes cancer that responds to hormone treatment.

A drooping lid and a small pupil on one side, signaling that the nerve chain running from the chest to the eye has been interrupted.

A program that provides special care for people who are near the end of life and for their families, either at home, in freestanding facilities, or within hospitals.

A cell that is infected by a virus or another type of microorganism.

A hot flash is a sudden sensation of body warmth, flushing, and sweating, most familiar with menopause but also linked to certain medications and conditions.

When radioactive material is used to examine the thyroid with a scanner, nodules that collect more radioactive material than the surrounding thyroid tissue are considered "hot." Hot nodules are…

Recurrence is what makes them useful, since a change seen repeatedly at one position is easier to test for and interpret.

A type of virus that can cause abnormal tissue growth (for example, warts) and other changes to cells.

A laboratory test in which cells are scraped from the cervix to look for DNA of human papillomaviruses (HPV).

A vaccine used to prevent genital warts, cervical cancer, vulvar cancer, and vaginal cancer caused by certain types of human papillomavirus (HPV).

A gene that may cause cancer when it is mutated (changed).

Three letters that in most conversations mean menopause, but that also cover thyroid, testosterone and gender-affirming treatment.

Cells of the uterine cervix that are moderately or severely abnormal and may become cancer.

HSV causes lifelong infection with two distinct types, one typically producing oral cold sores and the other typically producing genital sores.

A type of virus that infects T cells (a type of white blood cell) and can cause leukemia and lymphoma.

A monoclonal antibody that is being studied in the treatment of some types of cancer.

A monoclonal antibody being studied in the treatment of several types of cancer.

A Chinese herb that has been used as a treatment for a variety of medical problems.

A monoclonal antibody that binds to the protein MUC1, which is found on breast, ovarian, pancreatic, gastric, and colon cancer cells.

A monoclonal antibody being studied in the treatment of advanced multiple myeloma.

A substance being studied in the treatment of brain cancer.

A protein involved in normal cell growth.

A type of virus that causes herpes infections and has DNA as its genetic material.

A type of herpesvirus that may cause Kaposi sarcoma (a rare cancer that can cause skin lesions) and a type of lymphoma (cancer that begins in the lymph system), especially in patients who have a…

One of a group of proteins found on the surface of white blood cells and other cells that play an important part in the body's immune response to foreign substances.

Infection is close to universal and usually clears unnoticed, and it is the small share that persists which carries any cancer risk.

A laboratory test in which cells are scraped from the cervix to look for DNA of human papillomaviruses (HPV).

Built from empty shells of the virus coat, so it shows the immune system the right shape while containing no genetic material at all.

A type of virus that infects T cells (a type of white blood cell) and can cause leukemia and lymphoma.

A type of antibody made in the laboratory by combining a human antibody with a small part of a mouse or rat monoclonal antibody.

A drug used to treat chronic lymphocytic leukemia (CLL) that has not gotten better with other chemotherapy.

Adding water to air only helps within a range, since too little dries the airway and too much feeds mold and dust mites.

An uncommon type of thyroid tumor that can be benign or malignant.

A slow-growing tumor that develops from trophoblastic cells (cells that help an embryo attach to the uterus and help form the placenta) after fertilization of an egg by a sperm.

Hydration describes the body's water content and the medical practice of providing fluids to maintain or restore an adequate balance of water.

A substance made of only hydrogen and carbon.

The abnormal buildup of cerebrospinal fluid in the ventricles of the brain.

A drug used to treat moderate to severe pain and cough.

Hydrocortisone is a corticosteroid identical to the body's own cortisol, used both to replace a hormone shortfall and to calm inflammation and immune overactivity.

Hydrogen peroxide is a reactive compound used as a household disinfectant and, in concentrated forms, as an industrial bleaching or oxidizing agent.

Hydrolysis is a chemical reaction that uses water to break a larger molecule into smaller components, a process central to digestion.

Potency is both the point and the hazard, since a quantity that would suit morphine is far too much of this drug.

Swelling of the drainage spaces is a clue rather than a diagnosis, and it can linger after the blockage that produced it has gone.

Abnormal enlargement of the ureter caused by any blockage that prevents urine from draining into the bladder.

A drug that is used to treat many types of cancer and is being studied in the treatment of other types of cancer.

A substance that blocks an enzyme needed by the body to make cholesterol and lowers the amount of cholesterol in the blood.

Simple repeated habits such as handwashing and safe food handling block the routes by which infections travel between people and surfaces.

Activity above the normal level, whether that means a restless child or a gland working far too hard.

A form of nutrition that is delivered into a vein.

Calcium is held in a narrow range, and pushing it above that range makes nerves and muscles sluggish rather than excitable.

Radiation treatment in which the total dose of radiation is divided into small doses and treatments are given more than once a day.

Blood sugar rising is not felt at first, which is why the level is measured rather than judged from how a person feels.

An herbal product sold as an over-the-counter treatment for depression.

Hyperkeratosis is a thickening of the skin's outer keratin layer that can result from friction, chronic inflammation, or an inherited skin disorder.

The most common type of kidney cancer.

Overactive parathyroid glands pulling calcium out of bone and into the blood, often found on a routine test before symptoms appear.

More cells than there should be in a tissue, which is not the same thing as bigger cells or abnormal ones.

The damage comes from the response rather than the substance, as harmless proteins provoke a reaction built for parasites and pathogens.

Raised pressure rarely announces itself, so it is usually found on a routine check rather than because anything felt wrong.

Abnormally high body temperature.

Warming tissue a few degrees above normal to make tumor cells more vulnerable to the treatments given alongside it.

A procedure in which a warmed solution containing anticancer drugs is used to bathe, or is passed through the blood vessels of, the tissue or organ containing the tumor.

Hyperthyroidism speeds up the body's metabolism through excess thyroid hormone, most often caused by Graves disease, an autoimmune condition affecting the thyroid gland.

Hyperuricemia is an elevated blood level of uric acid that can result from increased production, reduced excretion, or both.

Hypervascular describes tissue or a lesion that contains an unusually high number of blood vessels compared with surrounding normal tissue.

Often blamed on nerves, but the same pattern is one of the earliest warnings of serious illness elsewhere in the body.

Responsiveness to suggestion is a fairly stable individual trait, and a minority of people barely respond to hypnotic technique at all.

Radiation treatment in which the total dose of radiation is divided into large doses and treatments are given less than once a day.

Radiation treatment in which the total dose of radiation is divided into large doses and treatments are given less than once a day.

A condition in which the level of immunoglobulins (antibodies) in the blood is low and the risk of infection is high.

Two symptom sets arrive in sequence, the adrenaline alarm first and confusion later, and the second is the one people cannot self-report.

Cancer that forms in tissues of the hypopharynx (the bottom part of the throat).

The last stretch of throat, where the paths of air and food finally part company and where cancer is often found late.

A birth defect in which the opening of the urethra (the tube through which urine leaves the body) is not in its normal place.

Blood pressure that is lower than expected for a person or situation.

The pituitary is called the master gland, yet it takes its orders from the structure sitting directly above it.

A study is built backward from it: the question decides the design, the number of participants, and what will count as an answer.