Urine Appearance in Undiagnosed Diabetes Insipidus
Yes, urine in undiagnosed diabetes insipidus is typically colorless or very pale, resembling water, because patients continuously produce maximally dilute urine with osmolality <200 mOsm/kg H₂O. 1
Pathophysiologic Basis for Colorless Urine
In diabetes insipidus, the kidneys cannot concentrate urine due to inadequate ADH secretion (central DI) or kidney resistance to ADH (nephrogenic DI), resulting in continuous production of maximally dilute urine with osmolality remaining <200 mOsm/kg H₂O regardless of fluid consumption. 1
The collecting tubules cannot respond to or lack ADH, leading to excretion of copious volumes of dilute urine that appears colorless or very pale yellow, similar to water. 1, 2
This dilute urine is pathognomonic for DI when combined with high-normal or elevated serum sodium—the triad of polyuria, polydipsia, and inappropriately dilute urine (osmolality <200 mOsm/kg H₂O) confirms the diagnosis. 1
Clinical Presentation Context
Patients with undiagnosed DI present with polyuria (>3 liters per 24 hours in adults), polydipsia, and inappropriately dilute urine that looks like water, combined with high-normal or elevated serum sodium. 1
The polyuria is not from excessive drinking but from the kidneys' inability to retain water, so patients must drink enormous volumes just to stay alive, which perpetuates the cycle of producing large volumes of colorless urine. 1
Children with undiagnosed DI present with polyuria, polydipsia, failure to thrive, and hypernatremic dehydration, with their urine appearing colorless due to the same concentrating defect. 1
Diagnostic Implications
The combination of urine osmolality <200 mOsm/kg H₂O (which produces colorless urine) with high-normal or elevated serum sodium confirms diabetes insipidus. 1
Urine osmolality definitively <200 mOsm/kg in the setting of serum hyperosmolality is required for diagnosis, and this degree of dilution produces urine that appears colorless or water-like. 3