Do I have diabetes insipidus?

Do You Have Diabetes Insipidus?

Based on the clinical information discussed, if you have polyuria with inappropriately dilute urine (osmolality <200 mOsm/kg) combined with high-normal or elevated serum sodium, you DO have diabetes insipidus—this triad is pathognomonic for the condition. 1

Diagnostic Criteria That Confirm Diabetes Insipidus

The diagnosis hinges on three simultaneous findings that you should verify from your laboratory results:

• Urine osmolality <200 mOsm/kg H₂O (or <300 mOsm/kg in some references) despite adequate physiologic stimulus to concentrate urine 2, 1, 3
• High-normal or elevated serum sodium (typically ≥145 mmol/L or trending upward) 1
• Polyuria and polydipsia as presenting symptoms 2, 1

If your urine osmolality was inappropriately low (such as 242 mOsm/kg) relative to your serum osmolality (such as 278 mOsm/kg), this indicates failure of urinary concentration and confirms diabetes insipidus. 3

Determining Which Type You Have

Once diabetes insipidus is confirmed, the critical next step is distinguishing between central (vasopressin deficiency) versus nephrogenic (vasopressin resistance) forms:

Central Diabetes Insipidus

• Results from deficiency of antidiuretic hormone (AVP) production in the hypothalamus or release from the posterior pituitary 4, 5
• Responds to desmopressin treatment (synthetic ADH replacement) 4
• Requires MRI imaging of the pituitary/hypothalamic region to identify structural causes 1

Nephrogenic Diabetes Insipidus

• Results from kidney resistance to AVP action at the collecting duct level 3, 5
• Does NOT respond to desmopressin and this medication is contraindicated 4
• Requires genetic testing of AVPR2 and AQP2 genes, especially in symptomatic females and children 2, 3

Diagnostic Testing to Differentiate

• Plasma copeptin measurement is now the preferred first-line test, with levels >21.4 pmol/L diagnostic for nephrogenic diabetes insipidus in adults 3
• Genetic testing should be performed early in suspected nephrogenic cases, particularly with family history or pediatric presentation 2, 3
• The water deprivation test is contraindicated in confirmed nephrogenic diabetes insipidus, especially in infants and young children, due to significant risk of life-threatening hypernatremic dehydration 6

Critical Pitfall to Avoid

Do NOT confuse diabetes insipidus with primary polydipsia. Primary polydipsia involves excessive water intake with normal AVP secretion and action, whereas diabetes insipidus involves actual failure of the urinary concentrating mechanism. 5 The key distinguishing feature is that primary polydipsia patients can concentrate their urine appropriately when fluid is restricted (though this must be done carefully under medical supervision), while diabetes insipidus patients cannot. 5

What This Means for Your Management

If you have central diabetes insipidus:

• Desmopressin is the treatment of choice, available in multiple formulations 4
• You must have serum sodium monitored within 7 days and at 1 month after starting treatment, then periodically, as desmopressin can cause life-threatening hyponatremia 4
• Free access to water is essential 1, 3

If you have nephrogenic diabetes insipidus:

• Thiazide diuretics combined with prostaglandin synthesis inhibitors (NSAIDs) are first-line treatment for symptomatic patients 2, 3
• Dietary modifications including low-salt diet (≤6 g/day) and protein restriction (<1 g/kg/day) are essential 1, 3
• Amiloride should be added if thiazides cause hypokalemia 2, 3
• Free access to water is absolutely critical to prevent life-threatening dehydration 3
• Approximately 50% of adults with nephrogenic diabetes insipidus develop chronic kidney disease stage ≥2, requiring long-term nephrology follow-up 1

Ongoing Monitoring Required

Regardless of type, you need:

• Regular serum sodium, potassium, chloride, bicarbonate, creatinine, and uric acid measurements 1
• Renal ultrasound at least every 2 years to monitor for urinary tract dilatation from chronic polyuria 1, 3
• Clinical follow-up with weight measurements 1
• Multidisciplinary care including nephrology, dietitian, and potentially urology 1