Osmolality

Clinical Chemistry

---

Description

Osmolality is a measure of the osmolar concentration of serum or urine. It is defined as the number of particles per kg of solvent. Essentially it is a measure of how concentrated the serum or urine is. The osmolality of the serum is mainly due to the concentration of sodium, chloride, urea and glucose. The osmolality of the serum is maintained within a narrow range in health. The osmolality of the urine varies greatly, mainly depending on hydration status.

---

Indications

Serum osmolality: 1. Investigation of hyponatraemia. 2. Investigation of potential poisioning/unconcious patient. Urine osmolality: 1. Investigation of hyponatraemia. 2. Investigation of polyuria (eg.?diabetes insipidus).

---

Sample Type

Serum. SST/Gel. minimum 2mL (1 mL separated serum). Urine (Fresh, No preservative).

---

Reference Range

Reference ranges are provided on the report. Alternatively, please contact the laboratory for current ranges.

---

Turnaround Time

Within 1 day

---

Testing Frequency

As Required

---

External Notes

Plasma osmolality changes as small as 1% are sometimes critical to a diagnosis of DI. We therefore recommend checking U&E and glucose with all plasma osmolality measurements so that osmolarity can also be calculated.

---

Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.