| Abbreviation | Definition |
|---|---|
| IRC | Incrementally Related Carrier |
| IRE | Internal Rotation in Extension |
| IRF | Internal Rotation in Flexion |
| IRIS | Immune Reconstitution Inflammatory Syndrome |
| IRMA | Intra-Retinal Microvascular Anomaly |
| IRP | Iron Regulatory Protein |
| IRS | Insulin Receptor Substrate |
| IRS | Insulin Resistance Syndrome |
| IRV | Ideal Resting Value |
| IRV | Inspiratory Reserve Volume |
| IS | In Situ |
| IS | Intercostal Space |
| IsA | Interstitial Acute |
| ISA | Intrinsic Sympathomimetic Activity |
| ISAC | Immune System Activation Of Coagulation |
| ISD | Intrinsic Sphincter Deficiency |
| ISDR | Interferon Sensitivity Determining Region |
| ISE | Initial Sensitizing Event |
| ISF | Interstitial Fluid |
| ISGP | International Society for Gravitational Physiology |