Medical abbreviations and acronyms (O)

This article contains a list of commonly used medical abbreviations and acronyms that start with the letter O and may be encountered in medicine and radiology (please keep the main list and any sublists in alphabetic order). 

A - B - C - D - E - F - G - H - I - J - K - L -M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z - misc

• O
  • blood type (ABO system)
  • oxygen
• O&G: obstetrics and gynaecology
• OA: osteoarthritis
• OAB: overactive bladder
• OAC: oral anticoagulant
• OAML: orbital adnexal MALT lymphoma
• OAR: organ at risk
• OAS: orbital apex syndrome
• OAT: osteochondral autograft transplantation 
• OB/GYN: obstetrics and gynaecology
• Obl: oblique
• Obs: observations
• OC
  • optic canal
  • optic chiasm
• OCA: osteochondral allograft transplantation
• OCD
  • obsessive-compulsive disorder
  • osteochondral defect
  • osteochondritis dissecans
• OCG: oral cholecystogram
• OCI: osteitis condensans ilii
• OCL: osteochondral lesion
• OCP
  • octacalcium phosphate
  • oral contraceptive pill
  • ova, cysts and parasites
• OCS: otic capsule sparing (temporal bone fractures)
• OCT: optical coherence tomography
• OCV: otic capsule violating (temporal bone fractures)
• OD
  • occupational disease
  • once daily (Latin: omne in die)
  • osteochondritis dissecans
  • overdose
  • right eye (Latin: oculus dexter)
• ODT: oroduodenal tube
• OE: otitis externa
• OE-MRI: oxygen-enhanced magnetic resonance imaging
• O/E: on examination
• OFC: osteitis fibrosa cystica
• OFD: occipitofrontal diameter
• OFDI: optical frequency domain imaging
• Og: oganesson
• OGD: oesophagogastroduodenoscopy
• OGT: orogastric tube
• OHCA: out-of-hospital cardiac arrest
• OHS: ovarian hyperstimulation syndrome
• OHSS: ovarian hyperstimulation syndrome
• OI
  • opportunistic infection
  • osteogenesis imperfecta
• OLIF: oblique lumbar interbody fusion
• OLLIF: oblique lateral lumbar interbody fusion
• OM
  • obtuse marginal artery
  • occipitomental
  • osteomalacia
  • osteomyelitis
  • otitis media
• om: every morning (Latin: omni mane)
• OMC: ostiomeatal complex
• OMU: ostiomeatal unit
• OMX: osteochondromyxoma
• ON:
  • take every night (drug prescriptions, Latin: omni nocte)
  • optic nerve
• ONH: optic nerve head
• O/N: overnight
• ONG: optic nerve glioma
• ONSD: optic nerve sheath diameter
• OOA: oesophageal obturator airway
• OOB: out of bed
• OOC: orthokeratinized odontogenic cyst
• OOH
  • out-of-hospital
  • out-of-hours
• OOHCA: out-of-hospital cardiac arrest
• OOHVFA: out-of-hospital ventricular fibrillation arrest
• OOP: out-of-plaster
• OP
  • operation
  • opinion
  • opposed phase
  • osteoporosis
  • out of phase
  • outpatient
• OPARACHEE: on resonance paramagnetic chemical exchange effect
• OPD: outpatient department
• OPG: orthopantomogram
• OPK: osteopoikilosis
• OPL: oblique posterior ligament
• OPLL: ossification of the posterior longitudinal ligament
• OPPT: orientated to person, place, and time
• OPT: orthopantomogram
• OPV: oral polio vaccine
• OR
  • odds ratio
  • operating room
  • organ at risk
• Ordercomms: order communications
• ORIF: open reduction internal fixation
• ORN: osteoradionecrosis
• ORSA: oxacillin-resistant staphylococcus aureus
• ORT: oral rehydration therapy
• OS: left eye (Latin: oculus sinister)
• Os: osmium
• OSA: obstructive sleep apnoea
• OSD
  • Occult spinal dysraphism
  • Osgood-Schlatter disease
• Osm
  • osmole
  • osmolarity
• OSNA: one step nucleic acid amplification
• OSP: oncocytic sinonasal papilloma
• OT
  • occupational therapy
  • optic tract
  • oxytocin
• OTC
  • oesophagotracheal combitube
  • on-table cholangiogram
  • over-the-counter (medication)
• OTD: out the door (discharge)
• OTTR: organ transplant tracking record
• OU
  • both eyes (Latin: oculus uterque)
• OV:
  • oesophageal varices
  • office visit
• oVEMP: ocular vestibular-evoked myogenic potentials
• OWR: Osler-Weber-Rendu syndrome
• OxyHb: oxygenated haemoglobin
• OYL: ossification of the yellow ligament
• oz: ounce (Italian: onza)