Urine osmolality is a test that is used to measure the amount of dissolved particles that are present in a person’s urine. It’s often used instead of specific gravity because the results are more accurate when attempting to determine the concentration of a person’s urine. This test is used to help diagnose diabetes insipidus, but may also be ordered to assess the hydration status of an individual who may be suffering from the symptoms of dehydration for any unknown reason.
Test results for diabetes insipidus urine osmolality are typically available within 24 hours, which means completing the process may take 48 hours in total once ordered by a medical provider.
What Are Normal Urine Osmolality Results?
There is a 24 hour collection procedure instituted for a vast majority of urine osmolality tests. On any random 24 hour test, the urine osmolality for a healthy individual should be between 500-800 mOsm/kg of water. The normal range for a laboratory may be between 300-900 mOsm/kg of water.
Age is also a factor. Once someone reaches the age of 20, the upper level of the normal range will typically decline by 5 mOsm/kg of water per year.
When testing for diabetes insipidus, fluid intake restrictions may also be ordered in conjunction with a urine osmolality test. In healthy individuals with fluid restrictions, after 12-14 hours, osmolality should exceed 850 mOsm/kg of water.
Based on these normal values, the test results reported by a laboratory may be higher or lower than normal. Healthy kidneys can create urine concentrations of up to 1,400 mOsm/kg of water or have a minimum concentration of 40 mOsm/kg of water, so a medical provider must interpret the results based on a patient’s health.
In general terms, however, here are the conditions that are associated with abnormal urine osmolality.
If There Is Decreased Urine Osmolality
The most common reason for decreased urine osmolality is an excessive level of fluids being consumed. This may also be achieved with high levels of caffeine intake throughout the day. When fluids are being regularly consumed or forced out of the body because of the action of a diuretic, this can dramatically lower urine osmolality without their being a health issue involved.
Diabetes insipidus urine osmolality is also typically much lower that the normal averages that are reported in this guide. Generally anything under 300 mOsm/kg of water is going to point toward this health condition, but results in the 200 mOsm/kg range is considered a hallmark for diabetes insipidus diagnosis.
Nephrogenic diabetes insipidus will typically have urine osmolality results that are less than 200 mOsm/kg of water even if the clinical signs are pointing toward hypovolemia, which is a decreased blood volume. Central diabetes insipidus will see similar results with water deprivation testing, but will correct itself with the introduction of vasopressin or desmopressin. Another urine osmolality test after hormone introduction may be required to confirm the effectiveness of the treatment.
Before diabetes insipidus will be diagnosed, however, a patient may need to be evaluated for Glomerulonephritis. This condition causes an acute inflammation of the kidney. It can happen for many reasons, but is often created by an immune response. This condition can be prolonged and build gradually like diabetes insipidus or be acute and severe.
If There Is Increased Urine Osmolality
The most common reason for an increased level of urine osmolality is the presence of dehydration. This may also be present when diabetes insipidus is the health issue involved if an individual is not consuming enough fluids. People who are eating a high protein diet may also have an increased level of urine osmolality.
Adrenal insufficiency, glycosuria, and high sodium levels are also known to cause increased urine osmolality levels. SIADH, or Syndrome of Inappropriate Anti-diuretic Hormone Secretion, may also be present if this is the test result.
What To Expect After Your Results Are Reported
The main goal of diabetes insipidus treatment is to avoid dehydration. Your medical provider will take the steps necessary to make sure your fluid intake is appropriate. This may mean changes to your diet, lifestyle changes, and taking medications or hormones to encourage healthy fluid retention.
Underlying conditions which may be causing abnormal urine osmolality levels will also need to be treated. Once these conditions are resolved, the diabetes insipidus may also resolve.
Because results are patient-specific and may be affected by a person’s medical history, only your medical provider can let you know what your diabetes insipidus urine osmolality results mean for you. Discuss what the normal values are, what your results were, and what that means for your health at your next appointment.