Glossary try the best to avoid the use of medical terms that could make it more difficult to understand the information on this website. Still, there are a number of terms that can't be avoided and that are useful to know because they are so often used by the doctors, nurses, and other medical professionals with whom you might speak. The list below includes the terms used on for which we have provided definitions.

Search for glossary terms (regular expression allowed)
Term Definition
Random Blood Sample

A sample of blood collected at any time of the day

Random Urine Sample

A sample of urine collected at any time of the day; this type of sample may be used to detect the presence of various substances in the urine at one particular point in the day. Often, no special handling is required with these samples. Other types of urine samples are requested when special types of evaluations are required (see 24-hour urine sample and timed urine sample).

Raynaud phenomenon

Intermittent episodes of pallor, cyanosis (bluing), and redness in the fingers or toes due to constricted blood vessels; it is seen with a variety of conditions and is precipitated by exposure to cold and emotional stress. It may cause numbness, tingling, and burning.


Substance used in performing a laboratory test

Recessive Gene

One of a pair of genes whose action is expressed only when two copies are present. For example, the gene for cystic fibrosis is recessive, and the disease will not occur if one normal gene is present.


The process by which a substance, such as bone, is broken down into basic components and removed from that area of the body


sensing part of the eye that collects images from the lens and translates them to chemical signals that can be interpreted by the brain

Reye syndrome

A rare condition that causes degeneration of the brain and is characterized by vomiting, fever, accumulation of fat in the liver, swelling of kidneys and brain, disorientation and coma; often occurs in children and following another illness, such as the flu or chickenpox.

Rheumatic fever

Condition resulting from an inadequately treated or untreated infection with Group A streptococcus bacteria. It is a delayed immune response in which the body produces antibodies directed against itself (autoimmune). This can cause serious damage to heart valves and lead to symptoms such as swelling and pain in several joints, heart inflammation (carditis), skin nodules, rapid, jerky movements (Sydenham's chorea), and skin rash.


A condition that occurs in childhood in which a severe lack of vitamin D causes weak, soft bones, delayed growth and skeletal development; when this condition occurs in adulthood, it is called osteomalacia.

Ribonucleic acid a nucleic acid present in all living cells. Its principal role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins although in some viruses RNA rather than DNA carries the genetic information.
Synonyms - Ribonucleic Acid

Also known as: Ribonucleic Acid

In a cell, a molecule that contains some of the genetic information of the cell involved in cellular processes and activities

RNA modification
RNA modifications are changes to the chemical composition of ribonucleic acid (RNA) molecules post-synthesis that have the potential to alter function or stability. An example of RNA modification is the addition of a methylated guanine nucleotide “cap” to the 5’-end of messenger RNAs (mRNAs).