In medical terminology, “AS” is an abbreviation with several different meanings depending on the context. The three most common uses are ankylosing spondylitis (a type of inflammatory arthritis), aortic stenosis (a heart valve condition), and auris sinistra (a Latin term meaning “left ear” used in prescriptions). Which meaning applies depends entirely on whether you’re reading a rheumatology report, a cardiology note, or a pharmacy label.
AS as Auris Sinistra (Left Ear)
On prescription labels and medication instructions, “AS” is shorthand for the Latin phrase auris sinistra, meaning left ear. You’ll see it most often on ear drop prescriptions. The related abbreviations are AD (auris dextra, right ear) and AU (auris utraque, both ears). However, many hospitals and pharmacies now discourage these Latin abbreviations because they’re easy to misread. The letter “a” can be mistaken for an “o,” which would change the meaning from an ear instruction to an eye instruction. Most providers now simply write “left ear” to avoid confusion.
AS as Ankylosing Spondylitis
Ankylosing spondylitis is a chronic inflammatory disease that primarily attacks the joints of the spine and pelvis. Over time, the inflammation can cause sections of the spine to fuse together, reducing flexibility and locking the back into a rigid posture. It belongs to a broader family of conditions called axial spondyloarthritis, which all involve inflammation where ligaments and tendons attach to bone.
Symptoms and Diagnosis
The hallmark symptom is low back pain that persists for three months or longer, improves with exercise, and is not relieved by rest. This pattern is the opposite of mechanical back pain from a muscle strain or disc problem, which typically feels better with rest and worse with activity. Other signs include limited range of motion in the lower back and reduced chest expansion compared to what’s normal for your age and sex.
Diagnosis requires imaging evidence of damage to the sacroiliac joints, the two joints connecting the base of the spine to the pelvis. A definitive diagnosis is made when X-rays show sacroiliac joint changes along with at least one of the clinical symptoms above. About 85% of people with ankylosing spondylitis carry a genetic marker called HLA-B27, though having this marker alone doesn’t mean you have the disease.
Treatment Approach
Exercise and physical therapy form the backbone of treatment. Regular movement helps maintain spinal flexibility and posture, while strengthening the muscles around the spine can reduce pain. When anti-inflammatory medications aren’t enough, biologic drugs that block specific inflammatory signals are the standard next step. These biologics target a protein called TNF, which drives much of the joint inflammation. For people with rapid disease progression or severe functional limitations, these medications can significantly slow the damage.
AS as Aortic Stenosis
Aortic stenosis is a narrowing of the aortic valve, the gateway between the heart’s main pumping chamber and the body’s largest artery. When this valve stiffens and narrows, the heart has to work harder to push blood through, and over time that extra effort takes a toll on the heart muscle. It’s one of the most common heart valve problems in older adults, affecting roughly 12% of people over age 75 to some degree. About 3.4% of that age group have severe narrowing.
Severity Levels
Doctors classify aortic stenosis by how much the valve opening has shrunk. A normal aortic valve opens to about 3 to 4 square centimeters. In mild stenosis, the opening is still greater than 1.5 square centimeters. Moderate stenosis means the opening has narrowed to between 1.1 and 1.5 square centimeters. Severe stenosis is anything below 1.0 square centimeter, at which point the heart is forcing blood through a space roughly the size of a pencil eraser.
What It Feels Like
Mild and even moderate aortic stenosis often cause no symptoms at all for years. The condition tends to progress slowly, with the valve narrowing a little more each year. Once it becomes severe, three classic symptoms tend to appear: chest pain (especially with exertion), shortness of breath, and fainting or dizziness. These symptoms signal that the heart can no longer compensate for the obstruction, and they typically mark the point where treatment becomes more urgent. The primary treatment for severe symptomatic aortic stenosis is valve replacement, either through open-heart surgery or a less invasive catheter-based procedure.
Less Common Uses of AS
In older medical literature, “AS” sometimes referred to Asperger’s syndrome, a developmental condition characterized by differences in social communication and restricted interests. Since 2013, Asperger’s syndrome is no longer a separate diagnosis. The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders folded it into the broader category of autism spectrum disorder. The change was driven by research showing that the old subcategories had poor diagnostic reliability and didn’t predict outcomes well. Some people still identify with the Asperger’s label, and you may encounter “AS” used this way in older records or community discussions.
Angelman syndrome is another rare condition sometimes abbreviated AS, though it’s more commonly written out in full to avoid confusion. It’s a genetic neurological disorder caused by loss of a specific gene on chromosome 15. In about 70% of cases, a deletion of the maternal copy of this chromosomal region is responsible. Angelman syndrome causes severe developmental delays, movement and balance problems, and a characteristically happy demeanor with frequent smiling and laughter.