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Formal name: Osmolality (plasma, urine, stool)

At a Glance

Why Get Tested?

To help evaluate the body's water and electrolyte balance; to investigate low sodium levels in the blood (hyponatremia) and increased or decreased urine production; to detect alcohol poisoning due to ingestion of toxins such as methanol or ethylene glycol; to monitor the effectiveness of treatment for conditions affecting osmolality; to help determine the cause of chronic diarrhea

When to Get Tested?

When someone has a low blood sodium level, is taking mannitol (an osmotic diuretic), may have ingested methanol, ethylene glycol, or isopropyl alcohol, is producing significantly increased or decreased amounts of urine, or has chronic diarrhea

Sample Required?

A blood sample drawn from a vein in your arm and/or a random urine sample; sometimes a fresh, liquid stool sample

Test Preparation Needed?

None may be required or you may be instructed to fast for 6 hours before the test; follow any instructions provided. Inform your health care provider of all medications you are taking, especially mannitol.