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 challenge being key diagnostic tools, as recommended by the international expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus 1.
Diagnostic Approach
The diagnostic approach for NDI involves:
- A thorough medical history focusing on symptoms like excessive thirst (polydipsia) and urination (polyuria)
- Basic laboratory tests including serum sodium, glucose, calcium, and kidney function tests
- The water deprivation test, where fluids are restricted under medical supervision while monitoring urine osmolality, specific gravity, and serum sodium
- A desmopressin challenge, where synthetic vasopressin (desmopressin) is administered; patients with NDI show minimal response to desmopressin, distinguishing it from central diabetes insipidus
Additional Tests
Additional tests may include:
- Measurement of plasma vasopressin levels, which are typically elevated in NDI
- Urinary aquaporin-2 excretion, which is reduced
- Genetic testing to identify mutations in the AVPR2 or AQP2 genes responsible for X-linked or autosomal forms of NDI
- Imaging studies like ultrasound or CT scans to rule out structural kidney abnormalities
Medication Review
Medication review is essential as drugs like lithium, demeclocycline, and certain antibiotics can cause acquired NDI, as highlighted in the international expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus 1.
Follow-up and Management
Follow-up and management of NDI involve:
- Regular monitoring of weight, height, and blood tests, including serum sodium, potassium, and creatinine levels
- Ad libitum access to fluid to prevent dehydration, hypernatraemia, growth failure, and constipation, as recommended by the international expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus 1
- Treatment with thiazide diuretics and prostaglandin synthesis inhibitors to reduce urine output, as recommended by the international expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus 1
- Surveillance imaging to detect hydronephrosis, bladder wall hypertrophy, and post-micturition urine residue, as recommended by the international expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus 1
From the Research
Diagnosis of Nephrogenic Diabetes Insipidus
To diagnose nephrogenic diabetes insipidus (NDI), the following methods can be used:
- Water deprivation test: This is considered the gold standard for diagnosis 2
- Baseline plasma copeptin measurement: A stable surrogate biomarker of AVP release, which can help in diagnosing NDI 3, 4
- Demonstration of subnormal ability to concentrate urine despite the presence of AVP: This is a key aspect of the clinical diagnosis of NDI 5
Diagnostic Considerations
When diagnosing NDI, it is essential to consider the following:
- Clinical manifestations of the disease, including symptoms such as polyuria and polydipsia 3, 6
- Etiology of the disease, including hereditary and acquired forms 3, 5, 6
- Differential diagnosis, including primary polydipsia and central diabetes insipidus 2, 4
Diagnostic Tests
The following diagnostic tests can be used to diagnose NDI:
- Water deprivation test followed by desmopressin administration: This is the gold standard for diagnosis 2
- Copeptin measurement: A stable and reliable surrogate marker for arginine vasopressin, which can help in diagnosing NDI 4
- Stimulation tests, such as hypertonic saline infusion or arginine infusion: These can be used to differentiate patients with central diabetes insipidus from patients with primary polydipsia 4