Medical records and prescriptions often contain a variety of shorthand notations that can appear confusing to a patient attempting to understand their own health information. This use of medical shorthand is a long-standing practice intended to ensure clarity, efficiency, and precision in documentation across different healthcare settings. When dealing with treatments for the ear, specific two-letter abbreviations are consistently used instead of writing out the words “right,” “left,” or “both.” This system of abbreviations is designed to standardize communication, which is particularly important when quick, unambiguous documentation is required. Understanding this unique language provides a clearer picture of the care being received and the instructions for medication use.
Decoding the Ear Abbreviations: AD, AS, and AU
The confusion over whether “AD” refers to the left or right ear is one of the most common questions patients have when reviewing medical documentation. This specific abbreviation, AD, definitively stands for the Right Ear in medical terminology. It is used universally in audiology and pharmacology to specify the side of the head being referenced for a condition or treatment.
The counterpart to AD is AS, which specifically designates the Left Ear. These two abbreviations are foundational for accurately describing unilateral (one-sided) hearing issues or for directing the application of medication to a single ear.
A third abbreviation, AU, is used when a condition or treatment involves both ears simultaneously. AU stands for Both Ears, indicating a bilateral issue or a treatment that must be applied to both sides. The use of these three distinct terms—AD, AS, and AU—is a simple, yet highly effective, method for ensuring that medical instructions are not misinterpreted.
It is especially important to differentiate between AD and AS because of the potential for medication errors if the wrong ear is treated. These standardized abbreviations prevent the kind of dangerous confusion that could arise from misreading handwritten text. The two-letter codes provide a consistent and easy-to-read signal for the exact location of treatment.
The Latin Roots Behind Medical Terminology
The reason these particular letters are used stems from a long history of medicine relying on the Latin language for its core terminology. Latin was historically the language of scholarship across Europe, allowing medical practitioners from different countries to communicate precisely. This tradition continues today, providing a universal foundation for many of the abbreviations found in clinical practice.
The “A” in all three abbreviations stands for the Latin word Auris, which translates directly to “ear.” This shared first letter provides an immediate context that the instruction relates to the auditory system. The second letter then indicates the specific side based on a corresponding Latin adjective.
AD is derived from Auris Dextra, where Dextra is the Latin word for “right.” Similarly, AS comes from Auris Sinistra, with Sinistra being the Latin word for “left.” The abbreviation for both ears, AU, is an abbreviation of Auris Utraque, where Utraque means “each” or “both.” This linguistic consistency provides a precise and unchanging reference point in medical communication.
How These Terms Are Used in Prescriptions and Audiology
The most frequent place a patient encounters AD, AS, or AU is on a prescription for ear drops or other topical ear treatments. A prescription label might contain the instruction “Instill 2 drops in AS twice daily,” which clearly instructs the patient to place two drops in the left ear in the morning and evening. This precise notation is necessary because many ear medications are designed to treat an infection or inflammation that is localized to only one side.
In audiology, these abbreviations are routinely used when documenting the results of hearing tests, known as audiograms. Hearing threshold levels, which indicate the quietest sounds a person can hear, are charted separately for each ear using these codes. For example, a chart might show results labeled AD and AS to clearly distinguish the hearing ability of the right ear from the left ear, which is fundamental to diagnosing and treating hearing loss.
The continued use of these Latin-based ear abbreviations is a deliberate safety measure, despite the move toward electronic prescribing. There is a well-known risk of confusion with abbreviations for the eyes: OD (Oculus Dextra for right eye), OS (Oculus Sinistra for left eye), and OU (Oculus Utraque for both eyes). Because the letters AD, AS, and AU can be easily misread as OD, OS, and OU, especially in handwritten notes, many healthcare institutions now recommend spelling out the full words “Right Ear,” “Left Ear,” or “Both Ears.”
However, because these abbreviations remain a standard component of many electronic health records and older prescription formats, understanding them remains a crucial step in patient literacy. The potential for a medication intended for the ear to be mistakenly placed in the eye, or vice versa, is a serious safety concern that these similar abbreviations highlight. Therefore, when encountering AD, AS, or AU on a prescription, patients should always confirm with their pharmacist or provider that the medication is indeed for the ear.