Water Deprivation Test Protocol for Diagnosing Diabetes Insipidus

Initial Assessment and Preparation

Measure baseline serum sodium, serum osmolality, urine volume, and urine osmolality in patients with polyuria-polydipsia syndrome to assess their hydration status and renal function 1
Consider measuring plasma copeptin levels as a surrogate marker for AVP, with levels <21.4 pmol/l prompting testing for AVP deficiency (central DI) in patients with suspected diabetes insipidus 1, 2
Rule out other causes of polyuria, including poorly controlled diabetes mellitus, by checking for hyperglycemia and glucosuria in patients undergoing the water deprivation test 3
Genetic testing may help distinguish between central DI and nephrogenic DI, especially in cases with partial AVP insensitivity, according to the Nature Reviews Nephrology guidelines 4, 2

Discontinue medications that can affect water metabolism, such as diuretics and prostaglandin inhibitors, at least 24 hours before the test to ensure accurate results, as recommended by the Nature Reviews Nephrology guidelines 5
Ensure a normal sodium diet (≤6 g/day) for several days before testing to minimize potential biases in the water deprivation test results 5
Administer desmopressin (DDAVP) after completing the water deprivation phase, and collect urine samples at 30, 60, and 120 minutes after DDAVP administration to assess the patient's response, as suggested by the Nature Reviews Nephrology guidelines 3, 1

For patients requiring fasting >4 hours, consider intravenous 5% dextrose in water at maintenance rate if needed, to prevent dehydration and electrolyte imbalances, according to the Nature Reviews Nephrology guidelines 3
Arginine stimulation test with copeptin measurement may be used as a confirmatory test for diabetes insipidus, with the response to desmopressin remaining a key differentiating factor between central and nephrogenic DI, as recommended by the Praxis Medical Insights guidelines 1, 2