From the Guidelines
Diabetes insipidus (DI) is characterized by polyuria, polydipsia, and dehydration, with laboratory findings including hypernatremia, high serum osmolality, and inappropriately dilute urine, and should be suspected in infants and children with polyuria, polydipsia, failure to thrive, and hypernatremic dehydration, and in adults with unexplained polyuria and polydipsia 1. The diagnosis of DI can be challenging, but a comprehensive family history and pedigree construction can help identify family cases, and initial work-up should include measuring serum sodium, serum osmolality, and urine osmolality, with inappropriately diluted urine and high-normal or elevated serum sodium being pathognomonic for the diagnosis of DI (nephrogenic or central) 1. Key symptoms of DI include:
- Excessive thirst with intake of 3-20 liters of water daily
- Frequent urination, including nocturia
- Preference for cold water
- Fatigue, muscle weakness, irritability, and dizziness from dehydration and electrolyte imbalances Genetic testing can provide an early and definite diagnosis, with important implications for clinical management and outcome, and can avoid unpleasant, challenging, and potentially harmful diagnostic procedures, including the desmopressin (DDAVP) test or the water deprivation test 1. We strongly recommend measuring serum sodium, serum osmolality, and urine osmolality as an initial biochemical work-up in patients with suspected nephrogenic DI (NDI) 1, and performing genetic testing in a laboratory accredited for diagnostic genetic testing, using a massively parallel sequencing-based multigene panel that includes at least AQP2, AVPR2, and AVP 1.
From the FDA Drug Label
Laboratory tests for monitoring the patient include urine volume and osmolality In some cases, plasma osmolality may be required. The main labs for monitoring Diabetes Insipidus include:
- Urine volume
- Urine osmolality
- Plasma osmolality (in some cases) The symptoms of Diabetes Insipidus are not directly mentioned in the drug label, however, the label does discuss the importance of monitoring urine volume and osmolality, which are key indicators of the condition. 2
From the Research
Diabetes Insipidus Symptoms
- Excretion of large amounts of hypotonic urine 3
- Polyuria and polydipsia, despite having normal or elevated plasma concentrations of arginine vasopressin (AVP) 4
- Markedly increased thirst and urination, which can be distressing and increase the risk of volume depletion and hypernatremia in severe situations 5
Diabetes Insipidus Labs
- Water deprivation test to differentiate between the various forms of hypotonic polyuria 3, 6
- Measurement of urine and serum osmolality 5, 6
- Baseline plasma copeptin measurement, a stable surrogate biomarker of AVP release 4
- Combination of < 400 mosmol/kg in urine and > 302 mosmol/kg in serum as a cut-off for the diagnosis of diabetes insipidus 6
Diagnosis and Differential Diagnosis
- A detailed medical history, physical examination, and imaging studies are needed to detect the aetiology of diabetes insipidus 3
- Differentiation between central diabetes insipidus, nephrogenic diabetes insipidus, gestational diabetes insipidus, and primary polydipsia is essential for effective treatment 3, 4, 7
- The water deprivation test and the baseline plasma copeptin measurement can help differentiate between the different types of diabetes insipidus 3, 4