This article contains a list of commonly used medical abbreviations and acronyms that start with the letter I and may be encountered in medicine and radiology (please keep both 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

• I

  • coagulation factor I (a.k.a. fibrinogen)

  • iodine

  • isoleucine (single-letter amino acid code)

  • olfactory nerve

  • one (Roman numeral)

  • segment 1 of the liver

• IA: intra-arterial

• IAA: interrupted aortic arch

• IABP: intra-aortic balloon pump

• IAC: internal auditory (or acoustic) canal

• IAH: intra-abdominal hypertension

• IAM: internal auditory (or acoustic) meatus

• IAP: inferior articular process (of vertebra)

• IAS: interatrial septum

• IASLC: International Association for the Study of Lung Cancer

• IBD: inflammatory bowel disease

• IBE: iliac branch endoprosthesis

• IBE-EVAR: iliac branch endoprosthesis endovascular aortic aneurysm repair

• IBM: inclusion body myositis

• IBP: inflammatory back pain

• IBS: irritable bowel syndrome

• IBUS: intrabronchial ultrasound

• IC

  • inspiratory capacity

  • interventional cardiology

• ICA

  • internal carotid artery

  • invasive coronary angiography

• ICAD: intracranial atherosclerotic disease

• ICANS: immune effector cell-associated neurotoxicity syndrome

• ICB: intracranial bleed

• ICC: intercostal catheter

• ICD

  • implantable cardioverter-defibrillator

  • impulse-control disorder

  • International Classification of Diseases

• ICH

  • intracerebral hemorrhage

  • intracranial hemorrhage

• ICHD-3: International Classification of Headache Disorders 3rd edition

• ICI

  • immune checkpoint inhibitor

  • intracervical insemination

• ICP: intracranial pressure

• ICRP: International Commission on Radiological Protection

• ICRU: International Commission on Radiation Units and Measurements

• ICSI: intracytoplasmic sperm injection

• ICU: intensive care unit (preferred term, a.k.a. ITU)

• ICV: ileocecal/ileocolic valve

• ID

  • identification

  • infectious diseases

  • Iselin disease

• I&D: incision and drainage

• IDA

  • iminodiacetic acid

  • iron deficiency anemia

• IDC

  • indwelling catheter

  • invasive ductal carcinoma

• IDCP: intraductal carcinomas of the prostate

• IDDM: insulin-dependent diabetes mellitus

• IDOR: International Day of Radiology

• IDR: iodine delivery rate

• IE

  • infective endocarditis

  • that is (Latin: id est)

• IECF: infective exacerbation of cystic fibrosis

• IEM: inborn error of metabolism

• IEP

  • image exchange portal (UK)

  • inferior end-plate (vertebral body)

  • interstitial edematous pancreatitis

• IF

  • immunofluorescence

  • incidental finding

  • index finger

• IFFI: intraperitoneal focal fat infarction

• IFI: invasive fungal infection

• IFN: interferon

• IFR: infection fatality rate 

• Ig: immunoglobulin

• IGHL: inferior glenohumeral ligament

• IGRA: interferon gamma release assay

• IGRT: image-guided radiotherapy 

• IGS: image-guided surgery

• IGTT: insulin and glucose tolerance test

• IH: inguinal hernia

• IHD

  • intrahepatic duct

  • ischemic heart disease

• IHC: immunohistochemistry

• IHE: integrating the healthcare enterprise

• IHT: interhospital transfer

• II

  • coagulation factor II (= thrombin)

  • image intensifier

  • intellectual impairment

  • optic nerve

  • segment II of the liver

  • two (Roman numeral)

• IIA: internal iliac artery

• IIH

  • idiopathic intracranial hypertension

  • indirect inguinal hernia

• III

  • coagulation factor III (= tissue factor)

  • oculomotor nerve

  • segment III of the liver

  • three (Roman numeral)

• IIM: idiopathic inflammatory myopathy

• IIP: idiopathic interstitial pneumonia

• IJD: inflammatory joint disease

• IIV: internal iliac vein

• IJV: internal jugular vein

• IJS: internal joint stabilizer

• IL: intralymphatic

• ILA: interstitial lung abnormality

• ILC: invasive lobular carcinoma

• ILD: interstitial lung disease

• Ile: isoleucine (three letter amino acid code)

• ILE: Ivor-Lewis esophagectomy

• ILGA: inferior lateral genicular artery

• ILI

  • influenza-like illness

  • inhalational lung injury

• ILO: Ivor-Lewis esophagectomy

• ILR: implantable loop recorder

• ILS: immediate life support

• IM

  • intestinal metaplasia

  • intramedullary

  • intramuscular

• IMA

  • inferior mesenteric artery

  • internal mammary artery

  • intermetatarsal angle

• IMBP: intramural blood pool

• IMG: international medical graduate

• IMGA: inferior medial genicular artery

• IMM: idiopathic inflammatory myopathy

• IMNM: immune-mediated necrotizing myopathy

• IMP: impression

• IMRT: intensity-modulated radiation therapy

• In

  • inch

  • indium

• INH: isoniazid (isonicotinylhydrazine)

• INN: International Nonproprietary Name

• INO: internuclear ophthalmoplegia

• iNPH: idiopathic normal pressure hydrocephalus

• INR

  • international normalized ratio

  • interventional neuroradiology(ist)

• Insp: inspiratory

• INX: infliximab

• IO

  • immuno-oncology

  • intestinal obstruction

  • intraosseous

• IOC: intraoperative cholangiogram

• IOF: inferior orbital fissure

• IOFB: intraocular foreign body

• IOL: intraocular lens implant

• IOP: interstitial edematous pancreatitis

• IOR: immature oocyte retrieval

• IOUS: intraoperative ultrasonography

• IOV: inferior ophthalmic vein

• IP

  • inpatient

  • in-phase

• IPAA: ileal pouch - anal anastomosis

• IPD: idiopathic Parkinson disease

• IPF: idiopathic pulmonary fibrosis

• IPG: implantable pulse generator

• IPHC: intraperitoneal hyperthermic chemoperfusion

• IPJ: interphalangeal joint

• IPMN: intraductal papillary mucinous neoplasm

• IPMT: intraductal papillary mucinous tumor

• IPNBD: intraductal papillary neoplasm of the bile duct

• IPP: inflatable penile prosthesis

• IPS: idiopathic pulmonary syndrome

• IPV: inactivated polio vaccine

• IQ: intelligence quotient

• IR

  • infrared

  • interventional radiology

  • inversion recovery

• IRA: ileorectal anastomosis

• IRDS: infant respiratory distress syndrome

• IRIS: immune reconstitution inflammatory syndrome

• IR(ME)R: Ionizing Radiation (Medical Exposure) Regulations (UK)

• IRR: Ionizing Radiation Regulations (UK)

• IRV: inspiratory reserve volume

• ISO: International Standards Organization

• ISQ: in status quo

• ISR: intra stent restenosis

• ISS

  • inferior sagittal sinus

  • injury severity score

  • international staging system (myeloma)

• ISUP: International Society of Urological Pathology

• IT

  • information technology

  • intrathecal

• ITA: internal thoracic artery

• ITB: iliotibial band

• ITI: intratubal insemination

• ITN: incidental thyroid nodules

• ITP: immune thrombocytopenia

• ITU: intensive therapy unit (a.k.a. ICU)

• IU: international unit

• IUCD: intrauterine contraceptive device (preferred to IUD)

• IUD

  • intrauterine death

  • intrauterine device (IUCD preferred, to avoid confusing with meaning above)

• IUGR: intrauterine growth retardation/restriction

• IUI: intrauterine insemination

• IUO: inflammation of unknown origin

• IUTD: immunisations up to date

• IV

  • four (Roman numeral)

  • intervertebral

  • intravenous

  • segment four of the liver

  • trochlear nerve

• IVC

  • inferior vena cava

  • inspiratory vital capacity

  • intravenous cannula

  • intravenous cholangiogram

• IVCF: inferior vena cava filter

• IVD: intervertebral disc

• IVDA: intravenous drug abuser

• IVDU: intravenous drug user (preferred to IVDA)

• IVF

  • intravenous fluid

  • in vitro fertilisation

• IVF/ET: in vitro fertilisation and embryo transfer

• IVIg: intravenous immunoglobulin

• IVH: intraventricular hemorrhage

• IVL: intravascular lymphoma

• IVMP: intravenous pulse methylprednisolone

• IVOC: intervertebral osteochondrosis

• IVP: intravenous pyelogram

• IVS: interventricular septum

• IVU: intravenous urography

• IVUS: intravascular ultrasound

• IWOB: increased work of breathing

• IX

  • coagulation factor IX (a.k.a. Christmas factor)

  • glossopharyngeal nerve

  • investigation

  • nine (Roman numeral)

• Ix: investigation