Diabetes Insipidus Diagnosis and Assessment

Diagnostic Criteria

• The American College of Physicians and the National Institute of Diabetes and Digestive and Kidney Diseases recommend that diabetes insipidus (DI) requires inappropriately dilute urine with osmolality definitively <200 mOsm/kg in the presence of serum hyperosmolality, with a pathognomonic triad of high-normal or elevated serum sodium, inappropriately dilute urine, and polyuria >3 liters per 24 hours in adults 1, 2, 3.
• The Endocrine Society suggests that the serum sodium of >145 mmol/L is typically required for the diagnosis of DI, combined with inappropriately dilute urine 1, 2, 3.

Diagnostic Tests

• The European Society of Endocrinology recommends measuring 24-hour urine volume accurately to document polyuria, with a threshold of >3 liters/24 hours in adults 3.
• The American Society of Nephrology suggests obtaining simultaneous measurements of serum sodium, serum osmolality, and urine osmolality during a period of polyuria to accurately assess the kidney's concentrating ability 2, 3.

Differential Diagnosis

• The International Society of Nephrology recommends differentiating central from nephrogenic DI by measuring plasma copeptin level, with a threshold of >21.4 pmol/L indicating nephrogenic DI 3, 6.
• The American Diabetes Association suggests that diabetes mellitus should be ruled out with proper fasting glucose or HbA1c testing, as diabetes mellitus causes polyuria through osmotic diuresis from glucosuria, not ADH deficiency 2, 4, 5.

Treatment and Management

• The National Institute of Diabetes and Digestive and Kidney Diseases recommends that patients with DI require free access to plain water at all times to prevent severe hypernatremic dehydration 2.
• The European Society of Endocrinology suggests that desmopressin trial can be used to differentiate central from nephrogenic DI, with response indicating central DI and no response indicating nephrogenic DI 2.