What urine osmolality is indicative of Diabetes Insipidus?

Diabetes Insipidus (DI) is characterized by an inability of the kidneys to concentrate urine, leading to a high volume of dilute urine. In patients with this condition, the urine osmolality tends to be low because the kidneys are excreting large amounts of water without retaining solutes.

When urine osmolality is measured, a value of less than 250 mOsm/kg indicates a degree of dilute urine that is consistent with DI. This low osmolality reflects the body's inability to concentrate urine due to insufficient action of the antidiuretic hormone (ADH) or resistance to it, leading to a high output of clear, concentrated urine.

Other ranges of urine osmolality, such as greater than 300 mOsm/kg or values around 250-300 mOsm/kg, suggest more concentrated urine which could be indicative of other conditions, such as dehydration or even different types of diuresis. In the case of DI, the hallmark characteristic is the presence of low urine osmolality, confirming the diagnosis and differentiating it from other possible causes of polyuria and polydipsia.