Assessment of Your Laboratory Results
Based on your laboratory values, you do NOT have diabetes insipidus (DI). Your results actually demonstrate normal renal concentrating ability and appropriate ADH function 1, 2.
Why You Don't Have Diabetes Insipidus
Your Laboratory Values Are Inconsistent with DI
Your urine osmolality of 220 mOsm/kg is appropriately concentrated given your clinical context. In true DI, urine osmolality remains below 200-250 mOsm/kg despite significant hypernatremia and hyperosmolality 1, 3. Your serum sodium of 143 mmol/L and serum osmolality of 295 mOsm/kg are both within normal ranges, indicating your body is maintaining water balance effectively 4, 5.
**Your ADH level of <0.8 pg/mL must be interpreted in the context of your serum osmolality.** At a serum osmolality of 295 mOsm/kg (which is normal), a low ADH level is physiologically appropriate 3. The kidneys don't need maximal ADH stimulation when serum osmolality is normal. In contrast, patients with central DI show inappropriately low ADH levels when serum osmolality is elevated (>300 mOsm/kg) 3, 6.
What True DI Looks Like
Central DI presents with severe polyuria (>3 liters/24 hours), persistent thirst, and inability to concentrate urine even during water deprivation. Classic laboratory findings include:
- Serum sodium >145 mmol/L (often >150 mmol/L) 1, 7
- Serum osmolality >300 mOsm/kg (often >310 mOsm/kg) 1, 3
- Urine osmolality <200-250 mOsm/kg despite hypernatremia 1, 3
- Inappropriately low ADH levels relative to elevated serum osmolality 3, 6
Your values don't meet any of these criteria. Your serum sodium and osmolality are normal, and your urine osmolality of 220 mOsm/kg is actually appropriate for someone in a normal hydration state 4, 5.
Understanding Your Results
The ADH-Osmolality Relationship
ADH secretion is tightly regulated by serum osmolality. When serum osmolality is normal (275-295 mOsm/kg), ADH levels should be low because the body doesn't need to conserve water 3, 6. Your low ADH level at a serum osmolality of 295 mOsm/kg represents normal physiology, not pathology 3.
In central DI, the problem is that ADH remains inappropriately low when serum osmolality rises above 300 mOsm/kg. This causes the kidneys to produce dilute urine despite the body's need to conserve water, leading to progressive hypernatremia and hyperosmolality 1, 3, 6.
Your Urine Osmolality Is Normal
A urine osmolality of 220 mOsm/kg falls within the normal range for someone who is adequately hydrated. The reference range of 150-1150 mOsm/kg reflects the kidney's ability to vary urine concentration based on hydration status 4. Your kidneys are appropriately producing moderately dilute urine because your serum osmolality is normal and you don't need maximal water conservation 5.
In DI, urine osmolality remains fixed below 200-250 mOsm/kg regardless of serum osmolality or hydration status. This is the hallmark of the disease—the inability to concentrate urine when needed 1, 3, 2.
Common Pitfalls in Interpreting These Tests
Never interpret ADH levels in isolation—they must be correlated with serum osmolality. A low ADH level is normal when serum osmolality is normal, but pathological when serum osmolality is elevated 3. This is the most common error in evaluating for DI 1.
Don't confuse normal physiological variation in urine osmolality with pathology. Urine osmolality varies widely throughout the day based on fluid intake, and values between 150-300 mOsm/kg are common in well-hydrated individuals 4, 5.
The diagnosis of DI requires demonstrating the inability to concentrate urine during water deprivation or in the presence of hypernatremia. Your normal serum sodium and osmolality indicate your kidneys are responding appropriately to your hydration status 1, 2.
What These Results Actually Show
Your results demonstrate normal osmoregulation and intact ADH-kidney axis. Your body is maintaining normal serum sodium and osmolality through appropriate ADH secretion and renal water handling 4, 5. There is no evidence of polyuria, hypernatremia, or inability to concentrate urine—the defining features of DI 1, 2, 6.
If you were experiencing symptoms like excessive thirst or urination, these would need to be evaluated for other causes. DI is definitively ruled out by your normal serum sodium, normal serum osmolality, and appropriate urine concentration 1, 3.