Analysis index

2 ml serum

2 ml heparin plasma (Stability in serum/plasma at 4°C – 8°C: Several days in a well-sealed container).

Division of serum/plasma from the blood cells is required as soon as possible, if possible within one hour.

280 mOsmol/kg – 295 mOsmol/kg

Hyponatremia, disorders of the electrolyte metabolism, progress checks of diabetes insipidus therapy

Osmolality of plasma is the concentration of all osmotically active particles relative to 1l solvent. In plasma this is mainly determined by sodium, glucose and urea- plasma protein contribution is insignificant. Determination serves the purpose of providing information about electrolytes and fluids. Generally, simultaneous measuring of sodium and osmolality in urine (spontaneous urine) is necessary. 

On suspicion of intoxication with low molecular substances, determining of the osmotic gap is effective. Here, the difference between the measured and the calculated osmolality (calculated osmolality – measured osmolality) is used. The latter can be determined using the following formula:

Osmolality (mmol/kg) = 1,86*sodium (mmol/l) + glucose (mmol/l) + urea (mmol/l) + 9