With a serum sodium of 141 mmol/L, normal urine osmolality (~498 mOsm/kg), normal serum osmolality (~301 mOsm/kg), normal copeptin and normal uric acid, could I have diabetes insipidus?

Assessment of Diabetes Insipidus with Normal Laboratory Values

With a serum sodium of 141 mmol/L, normal urine osmolality (498 mOsm/kg), normal serum osmolality (301 mOsm/kg), normal copeptin, and normal uric acid, you do not have diabetes insipidus.

Why Diabetes Insipidus is Excluded

Your laboratory profile is incompatible with any form of diabetes insipidus for several critical reasons:

Normal Serum Sodium and Osmolality

• Diabetes insipidus characteristically presents with hypernatremia (serum sodium >145 mmol/L) and hyperosmolality, not the normal values you demonstrate 1, 2
• Your serum sodium of 141 mmol/L falls within the normal range (135-145 mmol/L), whereas DI patients typically exceed 145 mmol/L due to free water losses 1
• Your serum osmolality of ~301 mOsm/kg is at the upper limit of normal (275-295 mOsm/kg) but does not reach the elevated levels seen in DI 3

Inappropriately Concentrated Urine

• Your urine osmolality of ~498 mOsm/kg indicates preserved urinary concentrating ability, which directly contradicts diabetes insipidus 1, 2
• In severe central or nephrogenic DI, urine osmolality remains below 250 mOsm/kg despite dehydration 1
• Even in partial DI, urine osmolality ranges between 250-750 mOsm/kg, but patients demonstrate inability to maximally concentrate urine during water deprivation 1
• Your kidneys are appropriately concentrating urine in response to normal physiologic stimuli, which would be impossible with significant DI 2

Normal Copeptin Levels

• Copeptin is secreted equimolarly with arginine vasopressin (AVP) and serves as a stable surrogate marker for AVP secretion 4, 5
• Normal copeptin levels definitively exclude central diabetes insipidus, where copeptin would be inappropriately low (<4.9 pmol/L) relative to serum osmolality 4, 5
• In nephrogenic DI, baseline copeptin levels are markedly elevated (>20 pmol/L) due to compensatory AVP hypersecretion in response to renal resistance 5
• Your normal copeptin indicates both appropriate AVP secretion and appropriate renal response to AVP 4

Normal Uric Acid

• While uric acid is not a primary diagnostic criterion for DI, normal levels support the absence of chronic volume depletion that would accompany untreated DI 6

Diagnostic Criteria You Do Not Meet

Diabetes insipidus requires hypotonic polyuria (>3 liters/24 hours in adults) that persists during water deprivation 1. The diagnostic hallmarks you lack include:

• Polyuria with urine osmolality <250 mOsm/kg in severe forms 1
• Hypernatremia (>145 mmol/L) as a consistent finding 1
• Inability to concentrate urine maximally during water deprivation test 1, 2
• **Low copeptin (<4.9 pmol/L)** in central DI or high copeptin (>20 pmol/L) in nephrogenic DI 4, 5

Clinical Interpretation

Your laboratory constellation—normal sodium, normal serum osmolality, appropriately concentrated urine (498 mOsm/kg), and normal copeptin—demonstrates intact hypothalamic-pituitary-renal axis function 2, 4. This profile indicates:

• Normal AVP synthesis and secretion (evidenced by normal copeptin) 4
• Normal renal response to AVP (evidenced by concentrated urine) 2
• Normal osmoregulation (evidenced by normal sodium and osmolality) 1

If you are experiencing polyuria or polydipsia despite these normal values, consider alternative diagnoses such as primary polydipsia (excessive water intake with normal AVP function), osmotic diuresis (glucose, urea), or medication effects 1, 2. However, the diagnosis of diabetes insipidus—whether central, nephrogenic, or gestational—is definitively excluded by your current laboratory profile 1, 2, 4.