Predictors of failure to respond to fluid restriction in SIAD in clinical practice; time to re-evaluate clinical guidelines?

Background: Fluid restriction is recommended as first line therapy for Syndrome of Inappropriate Antidiuresis (SIAD), despite of lack of good evidence base to support its use, and poor efficacy in clinical practice and in the literature.

Objective: We set out to determine how many patients with well-defined SIAD had pre-treatment criteria which would predict failure to fluid restriction.

Methods: This was a consecutive, prospective evaluation of 183 patients with a diagnosis of SIAD in two different hospitals. Full ascertainment of the diagnostic criteria for SIAD was obtained in all patients.

Results: About 47% of patients had a urine volume <1500 ml in 24 h, 41% had initial urine osmolality > 500 mOsm/kg, 26% a Furst-equation ratio > 1. About 59% had one criterion predicting failure to respond to fluid restriction, 37% two criteria, and 3% three criteria.

Conclusions: Our data suggest that up to 60% of patients with SIAD had criteria which recent clinical guidelines suggest would predict nonresponse to fluid restriction. This may explain why the recommended first line therapy for SIAD has been shown to be ineffective.