From the Guidelines
Nephrogenic diabetes insipidus (NDI) is diagnosed through a combination of clinical evaluation, laboratory tests, and specialized diagnostic procedures, with the water deprivation test and desmopressin administration being key diagnostic tools 1. The diagnosis of NDI begins with a thorough medical history and assessment of symptoms such as excessive urination (polyuria) and excessive thirst (polydipsia).
- Laboratory tests include measurement of serum sodium, which is often elevated, and urine osmolality, which is typically low despite concentrated blood.
- The key diagnostic test is the water deprivation test, where fluid intake is restricted under medical supervision to observe if the patient can concentrate urine appropriately.
- In NDI, urine remains dilute even after water restriction.
- This is followed by administration of desmopressin (DDAVP), a synthetic form of antidiuretic hormone.
- Patients with NDI show minimal or no increase in urine concentration after DDAVP, distinguishing it from central diabetes insipidus. Additional tests may include:
- Measurement of plasma vasopressin levels
- Genetic testing for mutations in the AVPR2 or AQP2 genes, particularly in congenital cases, as recommended by experts 1
- Imaging studies like ultrasound or CT scans may be performed to rule out structural kidney abnormalities. Medication history is crucial as NDI can be caused by drugs like lithium, demeclocycline, or certain antibiotics. Identifying the underlying cause is essential for appropriate management of this condition, and patients should have an emergency plan in place, including a letter explaining their diagnosis and advice regarding intravenous fluid management 1. It is also important to note that patients with NDI should have ad libitum access to fluid to prevent dehydration, hypernatraemia, growth failure, and constipation, with the determination of the optimal amount of fluid best left to their own thirst sensation 1.
From the Research
Diagnosis of Nephrogenic Diabetes Insipidus
To diagnose nephrogenic diabetes insipidus (NDI), several methods can be employed, including:
- Water deprivation test: This test is used to assess the kidney's ability to concentrate urine in response to dehydration 2, 3.
- Baseline plasma copeptin measurement: Copeptin is a stable surrogate biomarker of arginine vasopressin (AVP) release and can be used to aid in the diagnosis of NDI 4, 3.
- Urinary osmolality measurement: Patients with NDI will have a urinary osmolality of less than 300 mosm/kg H2O despite water deprivation 2.
- Administration of aqueous vasopressin: Patients with NDI will show little or no increase in urine osmolality in response to vasopressin administration 2.
Diagnostic Considerations
When diagnosing NDI, it is essential to consider the patient's symptoms, such as polyuria and polydipsia, and to distinguish NDI from other causes of hypotonic polyuria, including primary polydipsia 4, 3. The diagnosis of NDI should also take into account the underlying cause of the disease, which can be either congenital or acquired 2, 4, 5, 6.
Laboratory Tests
Laboratory tests, such as serum electrolyte measurements and urine analysis, can also be used to support the diagnosis of NDI 4, 5, 6.
Imaging Studies
Imaging studies, such as renal ultrasound, may be used to rule out obstructive uropathy as a cause of NDI 6.