| APUD | Zellen, die Amine decarboxilieren können (amine and precursor uptake and decarboxylation) |
| APZ | antigenpräsentierende Zelle |
| aq | aqua |
| ARA | American Rheumatism Association |
| ARC | AIDS-related complex |
| ARD | acute-respiratory-distress (Viren) |
| AR-DRGs | Australian Refined Diagnosis Related Groups |
| ARDS | adult respiratory distress syndrome |
| Arg | Arginin |
| ARPKD | autosomal rezessiv polycystic kidney disease |
| ARRT | American Registry of Radiologic Technologists |
| ARV | AIDS-assoziiertes Retrovirus |
| AS | Aminosäure |
| AS | Aortenstenose |
| AS | Asepsis/ Antisepsis |
| AS | Asperger-Syndrom |
| ASA | antisarkolemmaler Antikörper |
| ASA | Atriales septum aneurysma |
| ASAT | aspartat amino transferase |
| ASB | assisted spontaneous breathing |
| asc. | ascendens/ ascendierend (aufsteigend) |
| ASCUS | atypical squamous cells of undetermined significance |
| ASD | Vorhofseptumdefekt |
| ASD | Arbeitsgemeinschaft für strukturierte Diabetestherapie |
| ASE | Antistreptolysin Einheit |
| ASH | EKG: asymetrische Septumhypertrophie |
| ASH | American Society of Hematology |
| ASH | Alkoholische Steatohepatitis |
| ASHG | American Society of Human Genetics |
| ASK | Antistreptokinase |