From the Guidelines
Diagnosing diabetes insipidus involves suspecting the condition in patients with polyuria, polydipsia, and hypernatraemic dehydration, and then confirming it through measurements of serum sodium, serum osmolality, and urine osmolality, with inappropriately diluted urine and high-normal or elevated serum sodium being pathognomonic for the diagnosis. According to the international expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus 1, a comprehensive diagnostic approach includes:
- Suspecting diabetes insipidus in infants and children with polyuria, polydipsia, failure to thrive, and hypernatraemic dehydration, and in adults with unexplained polyuria and polydipsia
- Taking a comprehensive family history and constructing a pedigree to identify family cases
- Measuring serum sodium, serum osmolality, and urine osmolality as part of the initial work-up
- Identifying inappropriately diluted urine (urinary osmolality <200 mOsm/kg H2O) in combination with high-normal or elevated serum sodium as diagnostic for diabetes insipidus (nephrogenic or central)
- Considering early genetic testing if nephrogenic diabetes insipidus is suspected, as recommended by the expert consensus statement 1. Key diagnostic features of diabetes insipidus include polyuria, polydipsia, and hypernatraemic dehydration, with laboratory tests confirming the diagnosis by demonstrating inappropriately diluted urine and elevated serum sodium levels 1.
From the Research
Diagnosis of Diabetes Insipidus
To diagnose diabetes insipidus, several tests and methods can be employed. The key is to differentiate between central diabetes insipidus (CDI), nephrogenic diabetes insipidus (NDI), and primary polydipsia (PP).
- The water deprivation test is considered the gold standard for differentiating between CDI, NDI, and PP 2, 3, 4.
- This test measures urine osmolality after a period of water deprivation. A threshold for urine osmolality of >800 mOsmol/kg after water deprivation can yield a sensitivity and specificity of 96 and 100%, respectively, for diagnosing PP 2.
- Plasma arginine vasopressin (AVP) levels and copeptin measurements can also be useful in the diagnosis. Copeptin, in particular, has been suggested as a reliable alternative to AVP measurement due to its stability and ease of measurement 2, 3, 5.
- The measurement of thirst ratings can help differentiate between CDI and primary polydipsia 3.
- A simplified and improved fluid deprivation test has been proposed, which can effectively discriminate between diabetes insipidus and other polyuria syndromes with a sensitivity of 90% and specificity of 98% 4.
Diagnostic Criteria
The diagnostic criteria for diabetes insipidus include:
- Polyuria and polydipsia
- Low urine osmolality
- High serum osmolality
- Absence of other causes of polyuria and polydipsia
Laboratory Tests
Laboratory tests used in the diagnosis of diabetes insipidus include:
- Urine osmolality
- Serum osmolality
- Plasma AVP levels
- Copeptin measurements
- Water deprivation test
Clinical Evaluation
Clinical evaluation is also crucial in the diagnosis of diabetes insipidus, including:
- Medical history
- Physical examination
- Imaging of the hypothalamic-pituitary region
- Assessment of thirst appreciation and polyuria 5