plasma Osmolality

• Osmolality = concentration in mmol/kg (or mOsm/kg)
  • Osmolality is measured
• Osmolarity = concentration in mmol/L
  • Osmolarity is calculated

<aside> 💡 Plasma/urine osmolarity = 2 x Na + Urea + Glucose (mmol/L)

Normal range: 275-295 mmol/L

</aside>

Osmolar Gap: difference between measured and calculated osmolality

<aside> 💡 If osmolar gap is >10mmol/L, then another substance must be contributing to osmolality, eg:

• Ethanol
• Methanol
• Ethylene glycol
• Acetone </aside>

ADH

• Too much: SIADH
• Too little: Diabetes Insipidus

Electrolyte abnormalities

• Na+
• K+
• Ca++

Less important:

• Mg++