This protocol addresses the clinical situation in which a patient meets all established criteria for SIADH yet no underlying cause can be identified — or when a family history of hyponatremia is present and plasma arginine vasopressin (AVP) levels are unmeasurable.
The combination of full SIADH criteria with absent aetiology, a familial hyponatraemia pattern, or unmeasurable plasma AVP raises specific diagnostic and management considerations that differ meaningfully from typical SIADH.
Oral urea therapy is the primary approach in this setting; vaptans are generally not effective in this presentation. The complete protocol — including step-by-step guidance and monitoring parameters — is available below.
Clinical target: Normalization of the serum sodium concentration.
DOI: 10.1016/j.amjmed.2013.07.006
Suspicion for NSIAD should be raised when a patient meets all criteria for a diagnosis of SIADH (Table 2) without any apparent cause for the disorder or if there is a family history of hyponatremia; unmeasurable plasma AVP levels heighten suspicion, but confirmation of NSIAD requires sequencing of the V2R gene.
Although use of vaptans has not been tested in large numbers of patients with NSIAD, available data suggest that most such patients are unresponsive to vaptans; urea therapy is a reasonable alternative in these cases.
To date, vaptans have not been effective in the few patients with NSIAD in whom they have been tried, but urea therapy has been found to be effective in young children with this disorder.
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