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Osmolality Test

Medically reviewed by Last updated on Dec 2, 2022.

What does an osmolality test measure?

An osmolality test measures electrolytes, sugar, and waste products in your blood, urine, or bowel movement. Examples of electrolytes include sodium, potassium, and chloride. An example of a waste product includes urea.

Why do I need this test?

You may need an osmolality test for any of the following reasons:

  • Symptoms of low sodium levels, such as confusion, extreme thirst, headache, nausea, and seizures
  • More or less urination than usual
  • Currently taking medicine to decrease the amount of water or swelling in your body
  • Ate or drank something poisonous or toxic
  • Chronic diarrhea

How do I prepare for the test?

Your healthcare provider will tell you how to prepare for the test. The provider may tell you to stop eating and drinking 6 hours before the test. He or she may also tell you not to take certain medicines on the day of the test.

What do the results of the test mean?

The results of an osmolality test tell healthcare providers how well your body balances water with electrolytes, sugar, and waste products. The results of an osmolality test can help healthcare providers do the following:

  • Diagnose conditions that affect your hormone levels
  • Diagnose problems with your brain or kidneys
  • Decide if your medicines are working correctly

Care Agreement

You have the right to help plan your care. To help with this plan, you must learn about your lab tests. You can then discuss the results with your healthcare providers. Work with them to decide what care may be used to treat you. You always have the right to refuse treatment.The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.