| PFU | plaque-forming unit; pock-forming unit |
|---|---|
| PICU | pediatric intensive care unit; pulmonary intensive care unit |
| PSU | photosynthetic unit; primary sampling unit |
| PU | palindromic unit; passed urine; pepsin unit; peptic ulcer; pregnancy urine; 6-propyluracil; prostati... |
| RTU | real-time ultrasonography; relative time unit; renal transplantation unit |
| ISO | International Standard Organisation |
|---|---|
| ISAAC | International Study of Asthma and Allergies In Childhood |
| ISIS-2 | International Study of Infarct Survival |
| IUATLD | International Union Against Tuberculosis and Lung Disease |
| IUPAC | International Union of Pure and Applied Chemistry |