Would Undiagnosed Diabetes Insipidus Cause Thirst During Saline Administration?
Yes, if you had undiagnosed diabetes insipidus (DI), you would have been intensely thirsty during the saline drip, regardless of the IV fluids being administered. The absence of thirst during your 3-4 hour ER visit while receiving saline effectively rules out DI as a diagnosis.
Why DI Patients Experience Relentless Thirst
Patients with diabetes insipidus have intact and hypersensitive thirst mechanisms that drive them to drink enormous volumes of fluid continuously. 1, 2 The pathophysiology explains why:
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 <200 mOsm/kg H₂O 2
Patients produce 3+ liters of dilute urine per 24 hours regardless of fluid intake, because the collecting tubules cannot respond to or lack ADH 1, 2
The thirst mechanism in DI is typically MORE sensitive than normal, not less—studies show that 13 of 15 DI patients demonstrated progressive thirst ratings rising from 1.4 to 8.1 cm on visual analog scales during osmotic stimulation, with water intake significantly greater than controls 3
Why Saline Wouldn't Suppress Thirst in DI
Receiving isotonic saline intravenously would not eliminate thirst in a patient with DI because the fundamental problem is ongoing massive urinary water losses that IV fluids cannot keep pace with. 2
The polyuria in DI is not from excessive drinking but from the kidneys' inability to retain water—patients must drink enormous volumes just to stay alive 2
Even with IV saline running, a DI patient would continue losing free water through dilute urine faster than the IV could replace it, leading to rising serum sodium and intensifying thirst 1, 2
Research demonstrates that hypertonic saline infusion in DI patients causes plasma osmolality to rise from 292 to 316 mOsm/kg, triggering intense thirst (8.1/10 on visual analog scale) that is only relieved by drinking 3
Clinical Significance of Your Experience
Your lack of thirst during 3-4 hours without oral intake while receiving saline is strong evidence against DI. 1, 3
Patients with true DI require free access to fluids 24/7 to prevent life-threatening hypernatremic dehydration—they cannot tolerate even brief periods without drinking 1, 2
The thirst in DI is described as a dry, unpleasant tasting mouth that is only promptly relieved by drinking—IV fluids alone do not satisfy this sensation 4
Only 2 of 15 DI patients in research studies showed abnormal thirst perception (one hypodipsic, one with compulsive water drinking), and these patients had clinically significant abnormalities of salt and water balance 3
Common Pitfall to Avoid
Do not confuse diabetes insipidus with diabetes mellitus—DI involves normal blood glucose with inability to concentrate urine due to ADH deficiency or resistance, while diabetes mellitus involves elevated blood glucose causing osmotic diuresis through glucosuria 1
The diagnostic triad for DI is polyuria (>3 L/24h), polydipsia, and inappropriately dilute urine (osmolality <200 mOsm/kg) combined with high-normal or elevated serum sodium 1
If you had DI, you would have noticed extreme thirst and excessive urination long before your ER visit, typically producing several liters of clear, dilute urine daily 1, 5