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How does diabetes insipidus affect urine osmolality? – Medical News Today

Diabetes insipidus is a rare condition that affects the body’s ability to balance fluid levels properly. The condition can lead to excess urine production and low urine osmolality, which refers to the concentration of compounds in the urine.
Diabetes insipidus is a condition that causes the body to lose too much fluid through urination. It can lead to various complications, such as dehydration, fatigue, and fainting. As the condition causes a person to produce excessive amounts of urine, their urine will be excessively dilute, with a low urine osmolality.
In this article, we discuss diabetes insipidus and urine osmolality, including normal and abnormal ranges, additional tests to diagnose the condition, and management.
Also known as water diabetes, this rare condition interferes with the body’s ability to balance fluid levels. Worldwide, diabetes insipidus affects about 1 in 25,000 people, but evidence suggests that its prevalence is much higher in the United States.
Although the condition has a similar name to diabetes mellitus and may present with similar symptoms, the conditions are different. Diabetes mellitus affects blood sugar levels, whereas diabetes insipidus affects the kidneys’ ability to concentrate urine properly.
The kidneys filter water and excess fluid from the blood, which leaves the body through urine. Most of the fluid remains in the bloodstream. Vasopressin, also known as antidiuretic hormone, is responsible for helping the kidneys balance the amount of fluid and electrolytes in the body. However, if the body does not produce enough of this hormone, or does not respond to it, the kidneys are unable to concentrate urine properly.
Two main types of diabetes insipidus exist:
Central diabetes insipidus occurs when the body does not make enough vasopressin. The production of vasopressin occurs in the pituitary gland, which the hypothalamus controls. Central diabetes insipidus can occur when there is damage to the hypothalamus from a head injury, surgery, or a tumor. An inherited disease can also lead to central diabetes insipidus.
Nephrogenic diabetes insipidus occurs when the body produces enough vasopressin, but the kidneys do not respond properly to the hormone. This also results in the body producing too much urine. It can develop due to structural abnormalities that make the kidneys unable to respond to vasopressin.
The urine contains various components or particles. Urine osmolality refers to the concentration of these particles in the fluid. The compounds in urine include:
The correct balance of these compounds helps maintain the right balance of fluid in the body. A urine osmolality test involves obtaining a urine sample and analyzing it for the concentration of the compounds. It can help doctors diagnose electrolyte imbalances.
The kidneys typically control the entry of particles into the urine, which maintains the right fluid balance in the body. In people with diabetes insipidus, the lack of vasopressin or response to the hormone causes the kidneys to release too much water into the urine. This causes a large amount of urine with low urine concentration, or low urine osmolality. Essentially, the urine becomes too dilute.
Typically, a person will produce up to 2 quarts (qt) of urine daily, which is equivalent to about 1.9 liters (l). However, an individual living with diabetes insipidus may produce up to 20 qt, or 18.9 l, of urine per day.
The measurement of urine osmolality is typically in milliosmoles per kilogram of water (mOsm/kg). However, some experts may measure it in millimoles per kilogram (mmol/kg). These units have an equal conversion, meaning that 1 mOsm/kg is equal to 1 mmol/kg. Urine osmolality values can vary depending on a person’s hydration status, but most health experts consider a range of 50–1,200 mmol/kg normal.
As such, when testing urine osmolality, a doctor may also suggest a water deprivation test to help assess the body’s ability to concentrate urine when withholding fluids. When urine osmolality is less than 300 mOsm/kg, this may indicate diabetes insipidus.
Diabetes insipidus is a rare condition. As a result, its diagnosis can be challenging. Doctors typically begin by confirming the presence of hallmark symptoms, but the process will often involve ruling out other possible explanations for the symptoms.
The main symptoms of diabetes insipidus are the frequent urge to pass high volumes of low concentration urine and extreme thirst. Health experts may refer to these symptoms as polyuria and polydipsia, respectively. Other symptoms of diabetes insipidus may include:
Several tests may help confirm a diagnosis of diabetes insipidus. The National Institute of Diabetes and Digestive and Kidney Diseases notes that in addition to urinalysis, doctors may use the following tests:
Managing diabetes insipidus typically involves treating the underlying cause of the condition with the aim of relieving thirst and decreasing urine production.
In cases of central diabetes insipidus, a person may receive desmopressin (DDAVP), a synthetic version of vasopressin. This medication is available in many different forms, including as a tablet, injection, and nasal spray. DDAVP can help decrease urine output a few hours after administration, with this effect lasting for roughly 6–18 hours.
For individuals with nephrogenic diabetes insipidus, treatment will typically involve a sufficient fluid intake, a lower salt intake, and, possibly, the use of diuretics.
Diabetes insipidus is a rare condition that may affect the balance of fluid in the body. It occurs due to insufficient production of the antidiuretic hormone vasopressin or a lack of response to it. This results in an increase in urine production with a low osmolality. The management of the condition usually involves medication, changes to eating habits, and an adequate intake of fluids.
Last medically reviewed on July 28, 2022
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