Do You Have Diabetes Insipidus?
Based on your laboratory values, you do NOT have diabetes insipidus. Your urine osmolality of 220 mOsm/kg is above the diagnostic threshold, your serum sodium is normal, and your ADH level is appropriately detectable, all of which argue strongly against this diagnosis.
Why These Values Rule Out Diabetes Insipidus
The diagnostic criteria for diabetes insipidus require urine osmolality definitively <200 mOsm/kg in the setting of serum hyperosmolality or high-normal serum sodium—your urine osmolality of 220 mOsm/kg does not meet this threshold 1, 2.
Your serum sodium of 143 mmol/L is normal (not elevated), and your serum osmolality of 295 mOsm/kg is in the normal range (275-305), which does not indicate the hyperosmolar state expected in untreated DI 1.
The pathognomonic triad for diabetes insipidus is polyuria, polydipsia, and inappropriately dilute urine (osmolality <200 mOsm/kg) combined with high-normal or elevated serum sodium—you do not meet these criteria 1.
Your ADH level of 0.8 pg/mL (within the reference range of 0.0-4.7) indicates that you are producing antidiuretic hormone, which would be absent or very low in central diabetes insipidus 1, 3.
Understanding the Diagnostic Thresholds
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.
The European Urology guidelines confirm that a urine osmolality of 170 mOsm/kg would be inappropriately dilute in the presence of serum hyperosmolality, but your value of 220 mOsm/kg with normal serum osmolality does not fit this pattern 1.
In severe forms of DI, urine osmolality remains below 250 mOsm/kg and serum sodium is greater than 145 mmol/L—neither of which applies to your case 4.
What True Diabetes Insipidus Looks Like
Patients with actual diabetes insipidus typically present with polyuria (>3 liters per 24 hours in adults), polydipsia, and urine osmolality definitively <200 mOsm/kg 1, 4.
In central DI, ADH levels would be very low or undetectable, and in nephrogenic DI, plasma copeptin levels would be >21.4 pmol/L despite elevated ADH 1, 2, 3.
Patients with true DI who have free access to water maintain normal serum sodium at steady state because their intact thirst mechanism drives adequate fluid replacement—but they would still have markedly dilute urine (<200 mOsm/kg) 1.
Critical Distinction from Other Conditions
The diagnosis of diabetes insipidus requires simultaneous measurement of serum sodium, serum osmolality, and urine osmolality, with a threshold of polyuria >3 liters per 24 hours in adults 1.
If you are experiencing excessive thirst or urination, other causes should be investigated, including diabetes mellitus (which requires checking blood glucose levels first), primary polydipsia, or other renal concentrating defects 1, 4.
The water deprivation test followed by desmopressin administration remains the gold standard for diagnosis when DI is truly suspected, but your baseline values do not warrant this invasive testing 1, 5, 6.