Osmolality, Blood

This is a blood test which measures concentration of dissolved particles in the blood. As the amount of dilution with water increases or the amount of particles decrease (the osmolality or the concentration will decrease). This would be the same as putting a teaspoon of salt into a glass of water. If you increase the amount of water in the glass, then the osmolality would decrease. This test is used to determine fluid or electrolyte imbalance. The electrolytes are the ions or particles in your blood.

PREPARATION FOR TEST

No preparation or fasting is necessary.

NORMAL FINDINGS

  • Adult/elderly: 285-295 mOsm/kg H2O or 285-295 mmol/kg (SI units)

  • Child: 275-290 mOsm/kg H2O

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

Possible critical values

  • Less than 265 mOsm/kg H2O

  • Greater than 320 mOsm/kg H2O

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.