The Diagnostic Approach to the Patient with Hyponatremia: Are the Correct Investigations Being Done?

Numerous observational studies have confirmed that inadequate investigation of hyponatremia leads to diagnostic errors and incorrect treatment. In fact, only one out of five patients diagnosed as having syndrome of inappropriate antidiuresis (SIAD) have had all the tests necessary to meet the diagnostic criteria. Diagnostic errors could help explain why a majority of patients presenting hyponatremia during hospitalization are discharged while still hyponatremic. The correct differentiation of hypovolemic from euvolemic patients is a clinical diagnostic challenge. Yet the value of the physical examination in the volemic classification of the patient with hyponatremia has been reinforced by ultrasound studies revalidating the utility of the measurement of internal jugular vein pulse height in the clinical evaluation of intravascular volume. In this chapter, we review the data available on current approaches to the diagnosis of hyponatremia, and suggest our recommended approach to the evaluation of patients with hyponatremia, and more specifically, patients with SIAD. In addition, we will explore how specialized input from multidisciplinary hospital "hyponatremia teams," supported by technologies such as automated electronic alert systems, and computerized physician-support systems can aid the diagnostic pathway and clinical care delivery for patients with hyponatremia.