Do my labs (copeptin 4.6 pmol/L, urine osmolality 498 mOsm/kg, serum osmolality 301 mOsm/kg, serum sodium 141 mmol/L, normal glycated hemoglobin, creatinine, potassium, calcium, uric acid) and voiding ≤200 mL per episode suggest diabetes insipidus?

Your Laboratory Results Definitively Rule Out Diabetes Insipidus

Your urine osmolality of 498 mOsm/kg completely excludes diabetes insipidus, as this demonstrates excellent kidney concentrating ability—the opposite of what occurs in diabetes insipidus. 1

Why Diabetes Insipidus Is Not Present

Your laboratory values systematically exclude every diagnostic criterion for 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 feature of diabetes insipidus is inappropriately dilute urine (<200 mOsm/kg), which you clearly do not have. 2, 3

• Your copeptin level of 4.6 pmol/L is normal and falls well below the threshold of 21.4 pmol/L that would suggest nephrogenic diabetes insipidus. 1 This confirms your antidiuretic hormone (ADH) system is functioning normally.

• Your serum sodium of 141 mmol/L is normal, not elevated. 1 Diabetes insipidus typically presents with high-normal or elevated serum sodium (>145 mmol/L) when water access is restricted. 2, 3

• 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

The Diagnostic Triad You Do Not Meet

The pathognomonic triad of diabetes insipidus includes: 1, 2

• Polyuria (>3 liters/24 hours in adults)
• Inappropriately diluted urine (osmolality <200 mOsm/kg)
• Normal-high or elevated serum sodium

You meet none of these criteria. Your concentrated urine alone excludes the diagnosis.

Your Voiding Pattern Does Not Indicate Polyuria

• Voiding 200 mL or less per episode does not define polyuria. True polyuria requires measuring total 24-hour urine volume exceeding 3 liters per day in adults. 1, 2

• Frequent small voids can occur with overactive bladder, urinary tract issues, or simply frequent fluid intake with normal total output. This is fundamentally different from diabetes insipidus, where patients produce massive volumes of dilute urine. 4

Your Other Laboratory Values Are Normal

• HbA1c 5.4% rules out diabetes mellitus, which can cause polyuria through osmotic diuresis from glucose in the urine—a completely different mechanism than diabetes insipidus. 1

• Your creatinine (77 μmol/L), potassium (4.2 mmol/L), calcium (9.4 mg/dL), and uric acid (5.4 mg/dL) are all normal, further excluding alternative causes of urinary symptoms. 1

Critical Clinical Pitfall to Avoid

Do not proceed with a water deprivation test. When baseline testing shows urine osmolality >300 mOsm/kg with normal serum osmolality, performing a water deprivation test would be uncomfortable and potentially dangerous without adding any diagnostic value. 1

What to Investigate Instead

Since diabetes insipidus is excluded, consider alternative explanations for your symptoms: 1

• Measure 24-hour urine volume to objectively determine if true polyuria exists
• Evaluate for overactive bladder or other urological conditions
• Review medications that may affect urination patterns
• Assess fluid intake habits (excessive water drinking from habit rather than pathology)
• Consider primary polydipsia if excessive fluid intake is documented

Your kidneys are concentrating urine normally, your ADH system is intact, and you do not have diabetes insipidus.