Serum Osmolality

Blood Osmolality Test, Osmolality Test

Results

A serum osmolality test measures the amount of chemicals dissolved in the liquid part (serum) of the blood.

Normal

Normal values may vary from lab to lab. Results are usually available in about 4 hours.

Serum osmolality

Normal:	280–300 milliosmoles per kilogram (mOSm/kg) of water

High values

High serum osmolality levels may be caused by:

• Too little water in the body (dehydration).
• High levels of salt or sugar in the blood, such as poorly controlled diabetes and diabetic coma.
• A buildup of urea in the blood.
• Poisoning with certain substances, such as ethanol (the alcohol in alcoholic beverages), rubbing alcohol (isopropanol), wood alcohol (methanol), or antifreeze (ethylene glycol).
• A rare disease, such as diabetes insipidus, that causes the kidneys to produce large amounts of urine.

Low values

Low serum osmolality levels may be caused by:

• Too much water in the body (overhydration).
• A low level of salt in the blood.
• Overproduction of antidiuretic hormone (ADH) that may occur with some diseases, such as lung cancer.

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Author:	Maria G. Essig, MS, ELS Ralph Poore	Last Updated: January 29, 2008
Medical Review:	Anne C. Poinier, MD - Internal Medicine Caroline S. Rhoads, MD - Internal Medicine David C.W. Lau, MD, PhD, FRCPC - Endocrinology & Metabolism
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