From the Guidelines
The diagnostic workup for Diabetes Insipidus (DI) should begin with measuring serum sodium, serum osmolality, and urine osmolality as an initial biochemical work-up, as recommended by the most recent expert consensus statement 1. The initial evaluation of a patient with suspected DI involves assessing for symptoms such as polyuria, polydipsia, failure to thrive, and hypernatremic dehydration in infants and children, and unexplained polyuria and polydipsia in adults.
- A comprehensive family history and pedigree construction is essential to identify family cases, particularly for congenital nephrogenic DI.
- The detection of inappropriately diluted urine (urinary osmolality <200 mOsm/kg) in combination with high-normal or elevated serum sodium is pathognomonic for the diagnosis of DI (nephrogenic or central) and warrants early genetic testing if nephrogenic DI is suspected 1. Additional testing, such as a water deprivation test, can be considered to further evaluate the patient's response to dehydration and to differentiate between central and nephrogenic DI.
- Brain MRI is essential to evaluate for pituitary or hypothalamic lesions in central DI, particularly in patients presenting with new hormonal deficiencies or severe headaches, and in those with multiple endocrine abnormalities 1.
- Measurement of plasma vasopressin levels during the water deprivation test can further differentiate between central and nephrogenic DI, with low levels in central DI and high levels in nephrogenic DI. It is crucial to note that the diagnostic approach may vary depending on the clinical presentation and suspected underlying cause of DI, and a comprehensive evaluation should be tailored to each individual patient's needs.
From the Research
Diagnostic Workup for Diabetes Insipidus (DI)
The diagnostic workup for Diabetes Insipidus (DI) involves several steps to distinguish it from primary polydipsia and other causes of hypotonic polyuria. The key components of the diagnostic workup include:
- A thorough medical history to investigate nocturnal persistence of polyuria, onset and duration of the trouble, medication use, and potential hereditary nature of the disorder 2
- Weight and blood pressure measurements, and quantification of beverages and diuresis over a 24-hour cycle 2
- Assessment of signs of dehydration, bladder distention, pituitary hormone hyper- or hyposecretion, tumor chiasmatic syndrome, granulomatosis, and cancer 2
- Biological assessment, including urine osmolality and serum sodium levels 2, 3
- Pituitary magnetic resonance imaging (MRI) to investigate the lack of spontaneous hyperintensity signal in the posterior pituitary, which marks the absence of AVP and supports the diagnosis of central DI rather than primary polydipsia 2, 4
Diagnostic Tests
The diagnostic tests used to diagnose DI include:
- Water deprivation test, which is the gold standard for diagnosis, followed by desmopressin administration 5, 2, 4
- Desmopressin test to assess the response to ADH analogue 2
- Measurement of copeptin, a stable peptide reflecting AVP secretion, which can be a safer and faster biomarker for etiological diagnosis of polyuria-polydipsia syndrome 6
- Vasopressin or copeptin measurement to differentiate between central and nephrogenic DI 2, 6
Importance of Accurate Diagnosis
Accurate diagnosis of DI is crucial to provide appropriate treatment and prevent substantial morbidity and mortality. The treatment strategies vary depending on the type of DI, and application of the wrong treatment can be dangerous 3. A multidisciplinary team is generally recommended to provide management and monitoring of DI 4.