Bloods
Serum osmolality (Neonate: 270-290 mmol/kg Adult: 280-300 mmol/kg)
Calculated osmolality (mmol/L) = 1.86 (Na + K) + glucose + urea + 10.
Osmolar gap = measured osmolality minus calculated osmolality
Osmolality = mmol/kg of solvent
Osmolarity = mmol/L
>-<: Hb top, WCC L, Plt R, Hct bottom
-I-I-<: top - Na, Cl, Ur, bottom - K, HCO3, Cr < BSL
For Ca need ionised, and PTH to determine if acute or chronic