The AS medical abbreviation has three common meanings: left ear on a prescription, aortic stenosis in a heart record, and ankylosing spondylitis in a joint or spine record. The surrounding record, and whoever wrote it, decide which one applies.
On a drop order, AS comes from the Latin auris sinistra, left ear. It belongs to a set with AD for the right ear and AU for both ears. Those three look almost identical to the eye abbreviations OD, OS and OU, which is why safety groups ask staff to write the words instead. This page covers each meaning, sample lines, and the safer forms.
At a glance
Stands for
Left ear, from auris sinistra (pharmacy)Other meanings
Aortic stenosis (cardiology); ankylosing spondylitis (rheumatology)Safety status
Ear abbreviations are on the ISMP error-prone listSafer to write
Left earDo not confuse with
Where you see it
Ear drop orders, echo reports, rheumatology notes
AS medical abbreviation for the left ear
In pharmacy and ear, nose and throat care, AS marks the left ear as the place to put a medicine. The Latin roots are auris, ear, and sinistra, left. The full ear set is:
| Side | Ear form | Eye form |
|---|---|---|
| Right only | AD | OD |
| Left only | AS | OS |
| Both sides | AU | OU |
Prescription line: "Ofloxacin otic 5 drops AS BID x 7 days." Otic means for the ear, so this is an ear drop given into the left ear twice a day for a week. Treat it as an illustration of how such lines look, never as a dose.
Why left ear medical abbreviation forms are error-prone
AD, AS and AU are all flagged by ISMP, the national medication safety group, as error-prone shorthand. Handwritten, an A can look like an O, so AS can be read as OS and an ear drop put in the left eye. They can also be swapped with each other, sending a drop to the wrong ear.
The safer practice is to write left ear, right ear or both ears in full. Pharmacy labels almost always do this already, so a patient reading a label should see words, not letters. The medical abbreviation for left ear is still taught so students can recognize it on older or handwritten orders.
AS medical abbreviation in cardiology
In a heart record, AS means aortic stenosis: the aortic valve opening turns stiff and tight, which makes the heart work harder to push blood out to the body. It is often found as a murmur and confirmed with an echocardiogram. Reports grade it as mild, moderate or severe.
Echo report: "Severe AS, valve area 0.8 cm2, referred for valve replacement." Here AS clearly means the valve, not an ear. Treatment options for severe narrowing include surgery or a catheter procedure called TAVR.
Ankylosing spondylitis in rheumatology
Rheumatology notes use AS for ankylosing spondylitis, a long term inflammatory arthritis that mainly affects the spine and the joints where the spine meets the pelvis. It often starts in young adults with back pain and stiffness that is worse in the morning and eases with movement. A note might read "AS, HLA-B27 positive, on NSAID."
Nothing about ears or valves is involved there, and the surrounding words, such as back pain, sacroiliac joints or spine X-ray, make the meaning plain.
Telling the meanings apart
- Next to drops and the word otic: left ear.
- In an echo report, near murmur or valve: aortic stenosis.
- In a joint or back pain note: ankylosing spondylitis.
As a pharmacy abbreviation, AS is only ever the ear. In a problem list, it is almost always one of the two conditions. When a line truly could be read two ways, the writer or a pharmacist can settle it. Other route shorthand is collected in our prescription abbreviation guide.
This explains how the letters are used in general. For which ear, eye or condition applies to you, check the label wording and ask the pharmacist or clinician who wrote it.
Frequently asked questions
What does AS mean on ear drops?
On ear drops, AS means left ear, from the Latin auris sinistra. Most labels now print left ear in words because the letters are easy to misread.
Which abbreviation stands for the left ear?
The traditional abbreviation is AS. Safety groups recommend writing left ear in full so it is not confused with OS, the left eye.
What does AS mean in cardiology?
In cardiology, AS means aortic stenosis, a narrowed aortic valve. It is usually described as mild, moderate or severe based on an echocardiogram.
Is AS the same as OS?
No. AS means left ear and OS means left eye. The two are easily confused in handwriting, which is why ISMP flags both sets.
Can AS mean a back condition?
Yes. In rheumatology, AS means ankylosing spondylitis, an inflammatory arthritis of the spine. The setting of the note tells you which meaning applies.