| IOU | intensive care observation unit; international opacity unit |
|---|---|
| IRU | industrial rehabilitation unit; interferon reference unit |
| IU | immunizing unit; international unit; intrauterine; in utero; 5-iodouracil |
| KU | kallikrein unit; Karmen unit |
| LU | left upper [limb]; loudness unit; Lupron; lytic unit |