Osmolality serum test

This test may be done to:

• Check the balance between the water and the chemicals in your blood.
• Find out if you have severe dehydration or overhydration.
• Check to see if your body is making enough antidiuretic hormone (ADH).
• Find the cause of seizures or coma. In severe cases, these can be caused by an imbalance between water and electrolytes in the body.
• Find out if you have swallowed a poison, such as rubbing alcohol, wood alcohol, or antifreeze.

A health professional uses a needle to take a blood sample, usually from the arm.

In general, there's nothing you have to do before this test, unless your doctor tells you to.

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

High values

High levels may be caused by:

• Too little water in the body (dehydration).
• High levels of salt or sugar in the blood. This may be caused by problems such as poorly controlled diabetes.
• Damage to the kidneys. This can cause a buildup of urea in the blood.
• Poisoning with certain substances. These include ethanol (the alcohol in alcoholic drinks), rubbing alcohol (isopropanol), wood alcohol (methanol), and antifreeze (ethylene glycol).
• A rare disease, such as diabetes insipidus, that causes the kidneys to lose water and produce large amounts of urine.

Low values

Low levels may be caused by:

• Too much water in the body.
• A low level of salt in the blood. This can be caused by some medicines, including diuretics and certain blood pressure medicines.
• A condition called syndrome of inappropriate antidiuretic hormone secretion (SIADH). SIADH sometimes occurs with lung disease, cancer, diseases of the central nervous system, or the use of certain medicines.