Do I have diabetes insipidus given my normal copeptin (copeptin) level, normal serum osmolality, and normal urine osmolality, but experiencing urinary retention requiring self-catheterization (self-catheterization)?

You Do Not Have Diabetes Insipidus

Your laboratory results definitively exclude diabetes insipidus—your urine osmolality of 498 mOsm/kg demonstrates excellent renal concentrating ability, which is the complete opposite of what occurs in diabetes insipidus. 1

Why Your Results Rule Out Diabetes Insipidus

Diagnostic Criteria Not Met

Diabetes insipidus requires three specific findings simultaneously, none of which you have 1, 2, 3:

• Urine osmolality <200 mOsm/kg (yours is 498 mOsm/kg—more than double the threshold)
• Polyuria >3 liters per 24 hours (you don't mention this volume of urine output)
• High-normal or elevated serum sodium >145 mEq/L (your serum osmolality of 301 is normal, not elevated)

Your Copeptin Level is Normal

Your copeptin of 4.6 pmol/L is entirely normal and indicates appropriate ADH (antidiuretic hormone) secretion and kidney response 1. For comparison:

• Nephrogenic diabetes insipidus requires copeptin >21.4 pmol/L (yours is less than one-quarter of this threshold) 1, 2, 4
• Central diabetes insipidus would show copeptin <4.9 pmol/L even after osmotic stimulation (your level of 4.6 after mild overnight fasting is normal) 1

Your Kidneys Are Concentrating Urine Normally

The ability to concentrate urine to 498 mOsm/kg demonstrates that both your ADH secretion and kidney response are functioning normally 1, 2. In diabetes insipidus, urine osmolality would be definitively <200 mOsm/kg despite dehydration 1, 3.

What Your Symptoms Actually Suggest

Urological Dysfunction, Not Diabetes Insipidus

The fact that you required self-catheterization to obtain urine indicates urinary retention or bladder dysfunction, not diabetes insipidus 1. The American Urological Association recommends evaluation by a urologist for urinary frequency without true polyuria, as this suggests bladder dysfunction rather than a hormonal disorder 1.

Key Distinctions

• Diabetes insipidus causes excessive urine production (polyuria >3 liters/day with dilute urine)
• Your problem is difficulty emptying your bladder (urinary retention requiring catheterization)

These are opposite problems 1.

What You Should Do Next

Immediate Steps

1. Measure your actual 24-hour urine volume to document whether you truly have polyuria (>3 liters/24 hours) 2, 3
2. See a urologist for evaluation of your urinary retention and need for self-catheterization 1
3. Check fasting blood glucose to rule out diabetes mellitus, which can cause urinary symptoms through a completely different mechanism (osmotic diuresis from glucose) 1, 2

What to Monitor

If you're experiencing urinary frequency without large volumes, consider evaluation for 1:

• Overactive bladder
• Bladder outlet obstruction
• Neurogenic bladder
• Anxiety-related urinary frequency

Critical Pitfall to Avoid

Do not pursue diabetes insipidus workup or treatment based on these results—your laboratory values definitively exclude this diagnosis 1, 2, 3. Treating for diabetes insipidus when you don't have it could be dangerous, particularly if desmopressin were prescribed, as this can cause severe hyponatremia (dangerously low sodium) 2.