From the Guidelines
To investigate for diabetes insipidus, suspect the condition in patients presenting with polyuria, polydipsia, failure to thrive, and hypernatraemic dehydration, and proceed with measuring serum sodium, serum osmolality, and urine osmolality as the initial work-up. This approach is based on the latest recommendations from the international expert consensus statement on the diagnosis and management of congenital nephrogenic diabetes insipidus 1. The detection of inappropriately diluted urine, in combination with high-normal or elevated serum sodium, is pathognomonic for the diagnosis of diabetes insipidus and warrants early genetic testing if nephrogenic diabetes insipidus is suspected 1.
Key Diagnostic Steps
- Suspect diabetes insipidus in infants and children with polyuria, polydipsia, failure to thrive, and hypernatraemic dehydration, and in adults with unexplained polyuria and polydipsia 1
- Measure serum sodium, serum osmolality, and urine osmolality as the initial diagnostic tests 1
- Identify inappropriately diluted urine (urinary osmolality <200 mOsm/kg H2O) in combination with high-normal or elevated serum sodium as indicative of diabetes insipidus 1
- Consider comprehensive family history and pedigree construction to identify family cases, especially for congenital forms 1
Additional Investigations
- Genetic testing may be warranted early in the diagnosis process if nephrogenic diabetes insipidus is suspected 1
- Further tests such as the water deprivation test, desmopressin administration, and imaging studies like MRI of the brain may be necessary to differentiate between central and nephrogenic diabetes insipidus and to identify underlying causes [based on general medical knowledge, not directly stated in (1)].
By following this approach, clinicians can effectively investigate for diabetes insipidus, differentiate between its forms, and initiate appropriate management strategies to improve patient outcomes in terms of morbidity, mortality, and quality of life.
From the Research
Investigation for Diabetes Insipidus
To investigate for diabetes insipidus, the following steps can be taken:
- A thorough medical history is warranted to investigate nocturnal persistence of polyuria, specify the 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 can be useful 2.
- Assessment of signs of dehydration, bladder distention, pituitary hormone hyper- or hyposecretion, tumor chiasmatic syndrome, granulomatosis, and cancer is required 2.
- Biological assessment, pituitary magnetic resonance imaging (MRI), and results of a desmopressin test can aid in diagnosis 2.
- In severe forms of DI, urine osmolality remains below 250 mOsmol/kg and serum sodium greater than 145 mmol/L 2.
- The water deprivation test demonstrating the incapacity to obtain a maximal urine concentration is valuable, together with vasopressin or copeptin measurement 2, 3, 4.
- Pituitary MRI is done 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.
Diagnostic Tests
Diagnostic tests for diabetes insipidus include:
- Water deprivation test 2, 3, 4, 5
- Desmopressin test 2
- Pituitary magnetic resonance imaging (MRI) 2, 4
- Measurement of vasopressin or copeptin 2, 3, 4
- Hypertonic saline stimulation together with copeptin (or AVP) measurement 3
Differential Diagnosis
Differential diagnosis for diabetes insipidus includes: