What is Serum Osmolality (275-295)
| Level | Meaning | Investigation | DDx |
|---|---|---|---|
| Normal | Pseudohyponatremia: An extra non-osmotic agent is present (e.g. lipid, IG) | ‣, ‣ | ‣, ‣ |
| High | An extra osmotic agent is present (e.g. sugar → mannitol, sorbitol, urea, contrast) | ‣, ‣ | ‣ (fix sugar = fix Na) |
| Low | True (hypotonic) hyponatremia | Urine Sodium, Urine Osmolarity | RAAS problem vs. ADH problem |
| Mild | Moderate | Severe |
|---|---|---|
| Asymptomatic | Non-specific (nausea, confusion, headache) | !Seizure, ‣ |
| investigate first | investigate first | ‣ UNTIL neuro symptom resolves |
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| Urine Osmolarity) | ‣) | Interpretation | DDx (Etiology) | Treatment |
|---|---|---|---|---|
| ↓ - ADH is off | ↓ | ADH is on and it’s your fault | ‣, poor PO Na, protein intake (tea and toast diet) | ‣ |
| ↑ (> 100) - ADH is on | ↓ | ADH is on (inappripriate, as serum osm is low) | ‣, ‣, ‣, ‣ (RATS) | ‣ |