You Do Not Have Diabetes Insipidus
Your laboratory results definitively exclude diabetes insipidus—your urine osmolality of 498 mOsm/kg demonstrates excellent kidney concentrating ability, which is the opposite of what occurs in diabetes insipidus. 1
Why These Results Rule Out Diabetes Insipidus
Urine osmolality >300 mOsm/kg rules out diabetes insipidus, and your value of 498 mOsm/kg indicates normal kidney concentrating ability. 1
The pathognomonic triad of diabetes insipidus requires: (1) polyuria >3 liters/24 hours, (2) inappropriately dilute urine with osmolality <200 mOsm/kg, and (3) normal-high or elevated serum sodium—none of which are present in your case. 1, 2
Your serum osmolality of 301 mOsm/kg is only mildly elevated, and when combined with appropriately concentrated urine, this is completely inconsistent with diabetes insipidus. 1
Your copeptin level of 4.6 pmol/L falls within the normal reference range and is well below the threshold of 21.4 pmol/L that would suggest nephrogenic diabetes insipidus. 3, 1
Understanding Your Normal Results
Your serum sodium of 143 mEq/L is completely normal (not hypernatremia, which starts at >145 mEq/L). 1
The combination of normal serum sodium with concentrated urine after a 12-hour fast demonstrates that your vasopressin system and kidney concentrating mechanisms are functioning properly. 1
In true diabetes insipidus, urine osmolality remains below 250 mOsm/kg even during water deprivation, with serum sodium typically >145 mmol/L in severe forms. 2
Critical Clinical Pitfall to Avoid
Do not proceed with a formal water deprivation test when baseline testing shows urine osmolality >300 mOsm/kg with normal serum osmolality, as this would be uncomfortable and potentially dangerous without adding diagnostic value. 1
Many conditions can cause symptoms that mimic diabetes insipidus without actually representing the disease, including anxiety-related polydipsia, medications, or simply high fluid intake habits. 1, 4
What to Consider Instead
If you're experiencing urinary frequency or excessive thirst, investigate alternative causes such as primary polydipsia (excessive fluid intake driven by psychological factors or habit), anxiety, medications, or overactive bladder. 1, 4
Measuring 24-hour urine volume is essential to objectively quantify whether true polyuria (>3 liters/24 hours in adults) is even present. 1
Consider whether you're drinking excessively due to anxiety or habit rather than true physiological thirst—patients should drink to thirst rather than drinking excessively. 4