The differential diagnosis of CPO is shown in Table 1.
| Sign | CPO | COPD | Pneumonia | PE |
| Heart rate | ↑↑ | ↑ | ↑↑ | ↑↑ |
| Blood pressure | ↑ | → | ↓ | ↓ |
| Temperature | → | → | ↑ | → |
| O2 saturations | ↓↓ | ↓ | ↓ | ↓ |
| Chest signs | Bilateral crepitations | Diffuse wheeze | Focal crepitations | Clear |
| Skin | Cold, pale and clammy | Dry and warm | Flushed and warm | Dry |
| Heart sounds | Murmurs, 3rd/4th heart sounds | Normal | Normal | Normal |