Osmolality is a measure of the number of dissolved particles in a fluid. The osmolality test reflects the concentration of substances such as sodium, potassium, chloride, glucose, and urea in a sample of blood, urine, or sometimes stool. It is used to evaluate the balance between water and dissolved particles in the blood and urine, to detect the presence of substances that may affect this balance, and to assess the kidneys' ability to concentrate urine.
Blood osmolality is primarily a measure of sodium dissolved in the serum. Sodium is the major electrolyte in the blood, urine, and stool. It works with potassium, chloride, and CO2 (in the form of bicarbonate) to maintain electrical neutrality in the body and acid-base balance. Sodium comes into the body in the diet and is normally conserved or excreted in the urine by the kidneys to maintain its concentration in the blood within a healthy range.
Urine osmolality primarily measures the waste products urea and creatinine. Urea and creatinine are produced and removed by the body at a relatively constant rate.
Glucose and urea are not electrolytes but as particles (molecules), they do contribute to osmolality. Normally their contributions are small, but when someone has high blood glucose (hyperglycemia, as found in diabetes) or high blood urea (seen in diseases such as kidney failure), their influence can be significant.
Glucose is osmotically active. This means it can draw water out of the body's cells, increasing the amount of fluid in circulation, which in turn increases the amount of dilute urine produced. Mannitol, a drug used to treat cerebral edema, also has this property. Toxins such as methanol, isopropyl alcohol, ethylene glycol, propylene glycol, and acetone, and drugs such as acetylsalicylic acid (aspirin) can also affect osmolality when ingested in sufficiently large amounts.
A result lower than the normal range means you could have one of these conditions:
- Hyponatremia (too little sodium)
- Overhydration (too much fluid retained in the body)
Understand and improve your laboratory results with our health dashboard.
Upload your lab reports and get interpretation today.
Our technology helps to understand, combine, track, organize, and act on your medical lab test results.
A result higher than the normal range could point to one of these conditions:
- Hypernatremia (too much sodium)
- Diabetes insipidus (the kidneys make too much urine)
- Dehydration (low fluid levels throughout the body)
- Uremia (too much urea and other waste products in the blood)
- Hyperglycemia (high blood sugar)
Interpret Your Lab Results
Upload your lab report and we’ll interpret and provide you with recomendations today.
Get StartedGet Started With Our Personal Plan
Advanced Plan
Unlimited Plan
Are You a Health Professional?
Get started with our professional plan
Welcome to Healthmatters Pro.
Save time on interpreting lab results with the largest database of biomarkers online. In-depth research on any test at your fingertips, all stored and tracked in one place. Learn more
Pro Plan
for health professionals
$45 per month
At HealthMatters, we're committed to maintaining the security and confidentiality of your personal information. We've put industry-leading security standards in place to help protect against the loss, misuse, or alteration of the information under our control. We use procedural, physical, and electronic security methods designed to prevent unauthorized people from getting access to this information. Our internal code of conduct adds additional privacy protection. All data is backed up multiple times a day and encrypted using SSL certificates. See our Privacy Policy for more details.