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Osmolality Tests Test

Osmolality tests measure the concentration of particles like glucose, urea, and electrolytes in your blood, urine, or stool. They help check your body's fluid balance and how well your kidneys are working.

What this test measures

Osmolality tests measure the amount of certain substances (glucose, urea, and electrolytes such as sodium, potassium, and chloride) in your blood, urine, or stool. This shows the concentration of particles in your body fluid.

What your results mean

Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.

Higher-than-normal results

According to MedlinePlus, if your serum osmolality results are not normal, it may be a sign of dehydration, too much salt in the blood, antifreeze poisoning, diabetes insipidus, or stroke. For urine, it may indicate dehydration, heart failure, liver disease, or kidney disease.

Lower-than-normal results

According to MedlinePlus, if your serum osmolality results are not normal, it may be a sign of overhydration or too little salt in the blood. For urine, it may indicate overhydration.

Frequently asked questions

What is osmolality?

Osmolality is the concentration of particles dissolved in your body fluid. It is based on the amount of particles in a specific amount of that fluid.

What substances do osmolality tests measure?

They measure glucose, urea, and electrolytes such as sodium, potassium, and chloride.

Why might I need a blood osmolality test?

It is used to check the balance between water and certain substances in your blood, find out if you have swallowed poison like antifreeze, check for drug overdose, and help diagnose dehydration, overhydration, or diabetes insipidus.

What does a urine osmolality test check?

It is often used along with a serum osmolality test to check your body's fluid balance and to find the reason for increased or decreased urination.

What can cause abnormal stool osmolality results?

Abnormal stool osmolality may be a sign of factitious diarrhea (from overuse of laxatives) or malabsorption.

Related lab tests

Sources

Last updated . Information is aggregated from official public sources and is not a substitute for professional medical care.