| Abbreviation | Term(s) |
| A | Allergy |
| A | Annum |
| A | Anode |
| A | Anterior |
| A | Aortic |
| A | Artery |
| A | Axial |
| AB | Abort(miscarry) |
| AB | About |
| AB | Antibody |
| AB | Asthmatic bronchitis |
| ABD, ABDOM | Abdomen |
| ABN | Abnormal |
| ABP | Arterial blood pressure |
| ABST | Abstract |
| AC | Adrenal cortex |
| AC | Air contrast |
| AC | Anterior chamber |
| ACH | Adrenal cortical hormone |
| ACID PHOS | Acid phosphatase |
| ACID P'TASE | Acid phosphatase |
| ACTH | Adrenocorticotrophic hormone |
| ADENOCA | Adenocarcinoma |
| ADH | Antidiuretic hormone (vasopressin) |
| ADJ | Adjacent |
| ADM | Admission |
| ADM | Admit |
| AFF | Afferent |
| AFF | Affirmative |
| AFP | Alpha-fetoprotein |
| AG | Atrial gallop |
| AG | Antigen |
| AG | Argentum (silver, chemical symbol for) |
| AGL | Acute granulocytic leukemia |
| A/G RATIO | Albumin-globulin ratio |
| AGNO3 | Silver nitrate |
| AIDS | Acquired immunodeficiency syndrome |
| AK(A) | Above knee (amputation) |
| AKA | Also known as |
| ALB | Albumin |
| ALK PHOS | Alkaline phosphatase |
| ALL | Acute lymphocytic leukemia |
| AMA | Against medical advice |
| AMB | Ambulatory |
| AML | Acute myelogenous leukemia |
| AMP | Amputation |
| ANAP | Anaplastic |
| ANAT | Anatomy |
| ANES(TH) | Anesthesia, anesthetic |
| ANT | Anterior |
| ANTE | Before |
| A&P | Auscultation& percussion |
| AP | Abdominal perineal |
| AP | Anteroposterior |
| AP | Anterior pituitary |
| AP&LAT | Anteroposterior and lateral |
| APP | Appendix |
| APPROX | Approximately |
| ARC | Aids related complex |
| ARD(S) | Acute respiratory disease (syndrome) |
| ART | Artery(ial) |
| AS | Aortic stenosis |
| AS | Arteriosclerosis |
| ASCVD | Arteriosclerotic cardiovascular disease |
| ASHD | Arteriosclerotic heart disease |
| ASP | Aspiration |
| ASR | Aldosterone secretion rate |
| ASS | Anterior superior spine (of ilium) |
| A STEN | Aortic stenosis |
| ATP | Adenosine triphosphate |
| ATR | Achilles tendon reflex |
| ATR | Atrophy |
| AU | Angstrom unit |
| AU | Aurum (gold, chemical symbol for) |
| AUT | Autopsy |
| AV | Aortic valve |
| AV | Arteriovenous |
| AV | Atrioventricular |
| A & W | Alive and well |
| AX | Axilla(ry) |
| AX | Axis(dial) |