Osmolality Testing in Nephrology and How it Benefits Patients

December 8, 2021by scijo0

Osmolality testing is a crucial part of nephrology.

It can be done as a blood test or as an osmotic urine test, and it provides valuable information about the levels of osmotically active substances in your body.

This blog post will answer questions such as: what osmolality is, how it benefits patients, why you should have this test done, and who needs to be tested for osmolality levels.


What is osmolality testing in nephrology?

Osmolality testing is a measure of the osmotic pressure of a solution. It is used to determine how much water is in your blood and tissues.

This test is important for diagnosing and managing conditions such as dehydration, electrolyte abnormalities, and kidney disease.

Osmolality testing goes like this: osmolality is measured in milliosmoles per kilogram of water (mosmol/kg H20).

A plasma osmolality test is usually done first, and it measures osmolality in the bloodstream.

If this number is abnormal, an osmotic urine test may be done to measure osmolality in urine.

When choosing osmolality testing, an osmotic urine test is the more common one.

This involves collecting a small amount of your first morning urine in a special container.

Your osmolality test results are reported as the osmotic gap, which is calculated by subtracting your osmolality from plasma osmolality.


How does osmolality testing benefit patients?

Osmolality testing can help to diagnose and manage a variety of conditions.

It is especially important for patients with kidney disease, as it can help to monitor the progression of the disease.

Osmolality testing can also help to detect early signs of dehydration and electrolyte abnormalities.

Doctors usually use osmolality testing to determine if a patient has:

  • hyponatremia (low sodium levels) and hypernatremia (high sodium levels)
  • osmotic demyelination syndrome (central pontine myelinosis or osmotic demyelination myelinolysis)
  • psychogenic polydipsia (excessive water intake caused by psychological reasons, rather than medical ones) osmotic diuresis (increased urine output due to the presence of osmotically active substances in the body)
  • diabetes insipidus (a condition caused by the body’s inability to conserve water)
  • renal tubular acidosis (a disorder of the kidneys that results in the excretion of too much acid or too little bicarbonate in urine)
  • syndrome of inappropriate antidiuretic hormone (SIADH)
  • cerebral salt wasting syndrome (a condition that occurs when the brain loses too much sodium or osmotically active substances into cerebrospinal fluid)

Osmolality testing can also be used to monitor osmotic diuresis and osmotic demyelination syndrome.


Why should you have osmolality levels tested?

Osmolality testing is important because osmotic pressure can indicate the presence of other conditions.

If osmolality levels are too high, it may be a sign that you have water or salt imbalances.

Low osmolality readings generally mean that there is not enough water in your body and tissues.

It’s important to have osmolality testing done in order to detect and prevent these conditions.

An osmolality test can save your life.

For example, osmotic demyelination syndrome can cause irreversible damage to the brain if not detected early.

Especially if osmolality testing is ordered by your doctor, it’s important to have osmolality levels tested in order for the results to accurately reflect osmotic pressure in your bloodstream.


Who needs osmolality levels tested?

People who are at risk for kidney disease, dehydration, electrolyte abnormalities, or other issues should be tested osmotically.

Having this test can help you determine your osmotic pressure so that you can take steps to manage any conditions that may be present.

Speak with your doctor about whether osmolality testing is right for you.

Even if you don’t have any of the conditions listed above, osmolality testing may still be a good idea.

Annual osmolality testing is recommended for people over the age of 65, as osmotic pressure can increase due to a variety of factors.

However, osmolality testing is not recommended for pregnant women.

If you are pregnant and have concerns about osmotic pressure, consult with your doctor.



Osmolality testing is a simple, yet critical test that helps diagnose kidney disease.

It can be used to help determine the severity of your condition and develop an effective treatment plan for you – which can save you time and money in the long-term.

If it turns out that osmolality levels are high, this means there has been damage done to cells in your kidneys due to diseases like diabetes or chronic glomerulonephritis.

This will require complex medications such as immunosuppressants or chemotherapy drugs to control inflammation and prevent further cell damage from occurring.

For those who have normal osmolalities, they may need routine checkups on their blood pressure levels since these two conditions often go hand-in-hand.

Speak with your doctor to see if osmolality testing is right for you!

Leave a Reply

Your email address will not be published. Required fields are marked *