Your Laboratory Values Do Not Confirm Diabetes Insipidus
Based on your current laboratory values—particularly your urine osmolality of 220 mOsm/kg and normal ADH level—you do not meet diagnostic criteria for diabetes insipidus, though further evaluation is warranted given your polyuria. 1
Why This Is Not Classic Diabetes Insipidus
The diagnosis of diabetes insipidus requires urine osmolality definitively <200 mOsm/kg in the setting of serum hyperosmolality 1. Your values show:
- Urine osmolality of 220 mOsm/kg: This falls in an indeterminate range (200-300 mOsm/kg) that does not confirm DI 1
- Serum osmolality of 295 mOsm/kg: This is normal (reference 275-305), not elevated 1
- Serum sodium of 143 mmol/L: This is normal, not the hypernatremia (>145 mmol/L) typically seen in decompensated DI 2, 3
- ADH level of 0.8 pg/mL: This is normal (reference 0.0-4.7), arguing against central DI where ADH would be low or absent 1
Many conditions can cause urine osmolality in the 200-300 mOsm/kg range without representing true diabetes insipidus, including partial dehydration, chronic kidney disease, or early stages of various renal disorders 1.
What Your Results Actually Suggest
Your normal serum osmolality with normal sodium while producing dilute urine suggests one of several possibilities:
- Primary polydipsia (excessive fluid intake driving dilute urine) 3, 4
- Partial nephrogenic diabetes insipidus (incomplete form requiring further testing) 3
- High dietary sodium or protein intake temporarily increasing obligatory water excretion 1
The fact that your ADH is normal (0.8 pg/mL) is particularly important—in nephrogenic DI, ADH levels would be significantly elevated as the body attempts to compensate for renal resistance 2, 5. In central DI, ADH would be low or absent 5.
Required Next Steps for Definitive Diagnosis
You need a formal water deprivation test followed by desmopressin administration, which remains the gold standard for diagnosis 1, 3:
- Measure simultaneous serum sodium, serum osmolality, urine osmolality, and 24-hour urine volume under controlled conditions 1, 5
- Perform water deprivation test to demonstrate inability to concentrate urine maximally 3
- Administer desmopressin after water deprivation—response indicates central DI, no response indicates nephrogenic DI 2, 5
- Measure plasma copeptin levels as the primary differentiating test: levels >21.4 pmol/L indicate nephrogenic DI (elevated ADH), while levels <21.4 pmol/L suggest central DI or primary polydipsia 1, 5
Critical Considerations About Your Urine Output
Your reported output of "1L in 5 1/2 [hours]" extrapolates to approximately 4.4 liters per 24 hours, which does meet the threshold for polyuria (>3 liters per 24 hours in adults) 1, 3. However:
- Ensure accurate 24-hour urine collection by emptying your bladder completely at the start (discarding this urine), then collecting ALL urine for exactly 24 hours 1
- Maintain usual fluid intake based on thirst during collection—do not artificially restrict or increase fluids 1
- Avoid electrolyte-containing solutions like Pedialyte during testing, as these contain substantial sodium loads (1,035 mg/L) that can artificially increase urine output 1
What to Do Right Now
Do not restrict your water intake—this is a life-threatening error if you do have DI 1. Continue drinking to thirst while you pursue proper diagnostic evaluation 1.
Schedule formal testing with an endocrinologist or nephrologist who can perform controlled water deprivation testing and copeptin measurement 1, 5. If central DI is ultimately confirmed, you would need pituitary MRI with dedicated sella sequences to evaluate for structural causes 1, 5.
Your current laboratory snapshot is insufficient for diagnosis—the combination of normal serum osmolality, borderline urine osmolality (220 vs. required <200), and normal ADH levels does not establish diabetes insipidus 1, 5.