| Condition | Serum osmolality | Plasma sodium concentration by direct ion-selective electrode (point-of-care device or blood gas machine) |
| Hypotonic hyponatremia | Low¶ | Low |
Nonhypotonic hyponatremia due to endogenous solutes:
| High | Low |
Nonhypotonic hyponatremia due to exogenous solutes:
| Normal or high | Low |
Pseudohyponatremia
| Normal | Normal |
IV: intravenous; BUN: blood urea nitrogen.
* Therapeutic immunoglobulins are suspended in solutions of hypertonic maltose or sucrose that cause hyponatremia in a similar manner as IV mannitol; there may also be a small component of pseudohyponatremia due to the development of hyperproteinemia.
¶ Elevated BUN or blood alcohol levels can result in a misleadingly normal or high osmolality despite true hypotonic hyponatremia.
Δ Caused by elevated lipoprotein X levels.