There are multiple definitions:

1. arbitrary unit(English)

   • also denoted as a.u.
   • RU
   • Standards
   • https://doi.org…0268-013-0004-x

2. allergen unit(English)

   • Allergy

3. anterior uveitis(English)

   • the most common type of uveitis affecting the anterior segment of the eyes, including iris and ciliary body
   • AAU, RAAU
   • Ophthalmology
   • https://doi.org…598-021-91701-6

4. albuminuria(English)

   • a sign of incipient diabetic nephropathy if persistent
   • DM
   • Clinical chemistry, Nephrology, Diabetes
   • https://doi.org…198704010-01071

5. Agatston unit(English)

   • a semi-automated tool to calculate a score based on the extent of coronary artery calcification
   • CT
   • Calcium, Scoring systems/scales, Coronary circulation
   • https://doi.org…-3984.2015.0235

6. aquagenic urticaria(English)

   • a chronic inducible urticaria characterized by rapid development of hives following skin exposure to water. Lesions are 1-3 mm, perifollicular, pruritic wheals that spontaneously resolve within 30-60 minutes
   • SDAU
   • Dermatology, Allergy
   • https://doi.org…-9649.30.4.2183

7. alopecia universalis(Latin)

   • AA, AT
   • Dermatology
   • https://doi.org…155/2013/160203

8. antibiotic use(English)

   • AAD, AMS, AMU, CA, PD, VTH
   • Microbiology, Veterinary medicine
   • https://doi.org…1111/jvim.16814