Could my symptoms and lab results indicate undiagnosed diabetes insipidus?

Your Lab Results Do Not Support a Diagnosis of Diabetes Insipidus

Based on your laboratory values, you do not have diabetes insipidus. Your urine osmolality of 220 mOsm/kg is appropriately concentrated given your normal serum sodium (143 mEq/L) and serum osmolality (295 mOsm/kg), which rules out this diagnosis 1, 2.

Why Diabetes Insipidus Is Ruled Out

The diagnostic hallmark of diabetes insipidus requires urine osmolality definitively <200 mOsm/kg in the presence of high-normal or elevated serum sodium and serum osmolality 1, 2, 3. Your labs show:

• Urine osmolality: 220 mOsm/kg (above the diagnostic threshold of <200)
• Serum sodium: 143 mEq/L (normal range)
• Serum osmolality: 295 mOsm/kg (normal range 275-305)

The combination of appropriately concentrated urine relative to your normal serum osmolality effectively excludes diabetes insipidus 2, 3. In true diabetes insipidus, you would see inappropriately dilute urine (<200 mOsm/kg) despite elevated serum osmolality (>300 mOsm/kg), which is not your pattern 1, 2.

What Your Symptoms Actually Suggest

Your frequent urination with 64-96 oz daily water intake and 2-liter urine output represents normal physiologic response to your fluid intake 1. Consider these alternative explanations:

Primary Polydipsia (Excessive Fluid Intake)

• Drinking 64-96 oz (approximately 2-3 liters) daily naturally produces proportional urine output 1
• Your kidneys are appropriately diluting urine in response to this fluid load, evidenced by urine osmolality of 220 mOsm/kg 1
• Anxiety and stress can drive excessive fluid consumption 1

Possible Prediabetes or Early Diabetes Mellitus

Your glucose of 116 mg/dL after eating cookies 2 hours prior requires further evaluation 4. This warrants:

• Fasting plasma glucose (normal <100 mg/dL; prediabetes 100-125 mg/dL; diabetes ≥126 mg/dL) 4
• Hemoglobin A1C (normal <5.7%; prediabetes 5.7-6.4%; diabetes ≥6.5%) 4
• Diabetes mellitus causes polyuria through osmotic diuresis from glucosuria, not from ADH deficiency 1

Critical Pitfalls to Avoid

Do not pursue diabetes insipidus workup based on these labs 2. Many conditions cause urine osmolality in the 200-300 mOsm/kg range without representing diabetes insipidus, including partial dehydration, chronic kidney disease, or early renal disorders 1.

The water deprivation test or copeptin measurement would be inappropriate and potentially harmful in your case 1, 5, as your baseline labs already exclude the diagnosis.

Recommended Next Steps

1. Obtain fasting glucose and hemoglobin A1C to properly screen for diabetes mellitus 4
2. Track actual fluid intake versus output for 24-48 hours to document whether you're drinking excessively 1
3. Address anxiety and stress as potential drivers of excessive fluid consumption 1
4. Evaluate for other causes of urinary frequency such as overactive bladder, urinary tract infection, or prostate issues (if male) 1

Your low-normal potassium (3.2 mEq/L) should be corrected but does not indicate diabetes insipidus 1. Your BUN/creatinine ratio of 9 is normal and does not suggest dehydration 1.