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Glossaries - R

We've defined thousands of terms related to health care. This page discusses glossary terms with the letter R.

Randomized trial

a study in which participants are assigned by chance to one of two or more intervention arms or regimens. Randominization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms.

Randomized, double-blind, placebo-controlled, multicenter trial

a clinical trial in which patients have been randomly assigned to receive either the study drug or alternative treatment, in which neither the patient nor the physician(s) conducting the study know which treatment is being given the patient, and in which the alternative to the study drug is a placebo; the study is conducted at several center.

Range of motion (ROM)

The ability of a joint to go through all its normal movements. Range-of-motion exercises help increase or maintain flexibility and movement in muscles, tendons, ligaments, and joints.

Rapid Gastric Emptying (RAH-pid GAH-strik EM-tee-ying)


any chemical used in a laboratory test or experiment.


Areas on the outer part of a cell that allow the cell to join or bind with insulin that is in the blood. See also: Insulin receptors; a molecule on the surface of a cell that serves as a recognition or binding site for antigens, antibodies or other cellular or immunologic components.

Recombinant DNA (re-KOM-bih-nant)

DNA artificially constructed by insertion of foreign DNA into the DNA of an appropriate organism (usually bacteria or yeast) so that the foreign DNA is replicated along with the host DNA.

Recombinant Hirudin

A hirudin produced by recombinant DNA technology.

Rectal Manometry (REK-tul muh-NAW-muh-tree)

A test that uses a thin tube and balloon to measure pressure and movements of the rectal and anal sphincter muscles. Usually used to diagnose chronic constipation and fecal incontinence.

Rectal Prolapse (REK-tul PRO-laps)

A condition in which the rectum slips so that it protrudes from the anus.

Rectum (REK-tum)

The lower end of the large intestine, leading to the anus.

Reflux (REE-fluks)

A condition that occurs when gastric juices or small amounts of food from the stomach flow back into the esophagus and mouth. Also called regurgitation.

Reflux Esophagitis (REE-fluks uh-SAW-fuh-JY-tis)

Irritation of the esophagus because stomach contents flow back into the esophagus.

Regurgitation (ree-GUR-juh-TAY-shun)

See Reflux.

Relaxation therapy

People with arthritis use relaxation to release the tension in their muscles, which relieves pain.

Resectable (ree-SEK-tah-bill)

capable of being removed by surgery.


A disease of the small blood vessels in the retina of the eye.


a type of virus whose genetic material consists of RNA rather than the usual DNA; HIV and other viruses that carry their genetic material in the form of RNA rather than DNA and have the enzyme reverse transcriptase that can transcribe it into DNA. In most animals and plants, DNA is usually made into RNA, hence "retro" is used to indicate the opposite direction.

Reverse transcriptase

the enzyme produced by HIV and other retroviruses that enables them to direct a cell to synthesize DNA from their viral RNA.


an acute, potentially fatal disease of skeletal muscle.

Rheumatoid arthritis

An often chronic systemic disease that causes inflammatory changes in the synovium, or joint lining, that result in pain, stiffness, swelling, and loss of function in the joints. The disease can also affect other parts of the body.


A doctor who specializes in diagnosing and treating disorders that affect the joints, muscles, tendons, ligaments, and bones.


inflammation of the nasal mucosa (mucous membranes in the nasal cavities.

Risk factor

Anything that raises the chance that a person will get a disease. With noninsulin-dependent diabetes, people have a greater risk of getting the disease if they weigh a lot more (20 percent or more) than they should.

RNA (ribonucleic acid)

a single-stranded molecule composed of chemical building blocks, similar to DNA. The RNA segments in cells represent copies of portions of the DNA sequences in the nucleus. RNA is the sole genetic material of retroviruses.

Rotavirus (ROH-tuh-vy-rus)

The most common cause of infectious diarrhea in the United States, especially in children under age 2.

Rupture (RUP-tchur)

A break or tear in any organ or soft tissue.

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