2 Medical Prefixes

How prefixes shape medical terms

A prefix is a word part placed at the beginning of a medical term. It modifies the meaning of the root or combining form, often by describing location, direction, quantity, or condition. Not every medical term has a prefix.

Location and direction

These prefixes indicate where something is or how it is positioned or moving:

• sub- means under or below. Subcutaneous means beneath the skin; cutane means skin.

• endo- means within or inside. The endocardium is the inner layer of the heart; cardi means heart.

• peri- means around. Pericardial means pertaining to around the heart; cardi means heart and -al means pertaining to.

• inter- means between. Intercostal means between the ribs; cost means rib.

• intra- means within. Intravenous means within a vein; ven means vein.

• trans- means across or through. Transdermal means across or through the skin; derm means skin.

• ab- means away from. Abduction is movement away from the body's midline.

• ad- means toward. Adduction is movement toward the body's midline.

• retro- means behind or backward. Retrosternal means behind the breastbone; stern means breastbone.

Some location prefixes are easy to confuse: inter- means between, whereas intra- means within. Peri- means around, whereas endo- means within or inside.

Quantity, size, and degree

These prefixes describe number, amount, size, or degree:

• uni- and mono- mean one. Unilateral means one-sided; later means side.

• bi- means two or both. Bilateral means relating to both sides; later means side.

• hemi- and semi- mean half. Hemiplegia means paralysis affecting one side or half of the body; pleg means paralysis.

• tri- means three. Tricuspid means having three points or cusps; cuspid means point.

• multi- and poly- mean many and can sometimes mean excessive. Polyuria means an unusually large volume of urine; ur means urine.

• oligo- means few or scanty. Oliguria means low urine output; ur means urine.

• hyper- means above normal or excessive. Hyperglycemia means elevated blood glucose; glyc means sugar and -emia means blood condition.

• hypo- means below normal or deficient. Hypoglycemia means low blood glucose.

• macro- means large. Macrocyte means an unusually large cell; cyt means cell.

• micro- means small. Microcephaly means an unusually small head; cephal means head.

The meaning depends on the whole term. Hyper- and hypo- generally indicate a level above or below the expected range, while poly- can mean many or excessive.

Condition and rate

These prefixes describe a condition or rate:

• a- and an- mean without or absent. Apnea means a temporary absence of breathing; pnea means breathing.

• dys- means difficult, painful, or abnormal. Dysuria means painful or difficult urination; ur means urine.

• eu- means normal or good. Eupnea means normal, unlabored breathing.

• brady- means slow. Bradycardia means a slower-than-usual heart rate; cardi means heart and -ia means condition.

• tachy- means fast or rapid. Tachycardia means a faster-than-usual heart rate.

These prefixes describe a feature of a term; they do not by themselves establish a diagnosis. For example, bradycardia describes a slow heart rate, but whether it is a medical problem depends on the person and context.

Decode a term from its parts

To decode an unfamiliar medical term, combine its parts rather than relying on the prefix alone:

1. Identify the prefix at the beginning, if present.

2. Find the root or combining form that names the body structure or subject.

3. Check the suffix for a condition, procedure, or other meaning.

4. Combine the parts into a plain-language definition, then confirm that it makes sense in context.

For example, pericardial breaks down as peri- (around) + cardi (heart) + -al (pertaining to), giving “pertaining to around the heart.” In hypoglycemia, hypo- (low) + glyc (sugar) + -emia (blood condition) gives “a condition of low blood sugar in the blood.” These word-part meanings are useful clues, but an established medical meaning may be more specific than a literal word-by-word translation.

Recognizing prefixes helps make unfamiliar terms easier to decode, but combine the prefix with the root and suffix before deciding what the full term means.