Do You Have Diabetes Insipidus?
Based on your laboratory values, you do NOT meet diagnostic criteria for diabetes insipidus. Your serum sodium (143 mEq/L) is only minimally elevated, your serum osmolality (295 mOsm/kg) is normal, and critically, your urine osmolality (220 mOsm/kg) is above the diagnostic threshold for DI 1.
Why This Is Not Diabetes Insipidus
Urine osmolality is too high: The diagnosis of DI requires urine osmolality definitively <200 mOsm/kg in the setting of serum hyperosmolality 1. Your value of 220 mOsm/kg falls outside this diagnostic criterion.
Serum osmolality is normal: DI is characterized by inappropriately dilute urine combined with high-normal or elevated serum osmolality 1. Your serum osmolality of 295 mOsm/kg is well within the normal reference range (275-305 mOsm/kg).
ADH level is normal: Your ADH of 0.8 pg/mL is within the normal reference range (0.0-4.7 pg/mL), which argues against central DI where ADH would be inappropriately low for the serum osmolality 2, 3.
The "gray zone" problem: 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 Numbers Actually Show
Your kidneys ARE concentrating urine to some degree (220 mOsm/kg is more concentrated than plasma), which would not occur in true DI 1, 2.
The combination of normal serum osmolality, normal ADH, and urine osmolality >200 mOsm/kg suggests your kidneys are responding appropriately to ADH 1, 4.
Your urine output of 1 liter in 5.5 hours (approximately 4.4 liters per 24 hours if sustained) does represent polyuria (>3 liters per 24 hours in adults), but polyuria alone does not equal DI 1.
What You Should Do Next
If polyuria persists, you need proper diagnostic testing:
24-hour urine collection: This is essential to accurately quantify your true daily urine output, as spot measurements can be misleading 1. The collection must include ALL urine over exactly 24 hours, with the bladder emptied and discarded at the start, then all subsequent urine collected including the final void 1.
Simultaneous measurements: Obtain serum sodium, serum osmolality, and urine osmolality at the same time to assess the relationship between these values 1, 4.
Rule out diabetes mellitus FIRST: Check fasting blood glucose to exclude diabetes mellitus, which causes polyuria through osmotic diuresis from glucose spilling into urine (fasting glucose ≥126 mg/dL or random glucose ≥200 mg/dL with symptoms) 1.
Water deprivation test: If initial testing remains equivocal and polyuria persists, a formal water deprivation test followed by desmopressin administration remains the gold standard for diagnosis 1, 3, 4.
Copeptin measurement: Plasma copeptin levels can distinguish between central DI (copeptin <21.4 pmol/L) and nephrogenic DI (copeptin >21.4 pmol/L) if DI is confirmed 1, 4.
Critical Pitfalls to Avoid
Do not restrict water intake: If you do have DI (which your current labs do not support), restricting water access is life-threatening and leads to severe hypernatremic dehydration 1, 5.
Avoid electrolyte solutions during testing: When collecting 24-hour urine or undergoing diagnostic testing, drink only plain water or usual beverages, not electrolyte-containing solutions like Pedialyte, as these contain substantial sodium loads (approximately 1,035 mg per liter) that can confound results 1.
Consider other causes of polyuria: Excessive caffeine intake, uncontrolled diabetes mellitus, hypercalcemia, hypokalemia, certain medications (diuretics, lithium), and primary polydipsia (excessive water drinking) can all cause polyuria without DI 2, 4.