| OI | Opportunistic infections |
|---|---|
| OI | Orthostatic Intolerance |
| OI | Oxygenation Index |
| OIA | Optical ImmunoAssay |
| OIE | Office International des Epizooties |
| OIG | of Inspector General |
| OIG | of the Inspector General |
| OIH | 131I-orthiodohippurate |
| OIH | Orthoiodohippurate |
| OIR | Oxygen-induced retinopathy |