Abstract: SA-OR49
Critical Appraisal of Volume Status, Urine Sodium Concentration, and Urine Osmolality in the Differential Diagnosis of Hypotonic Hyponatremia
Session Information
- Fluid, Electrolyte, and Acid-Base Disorders: Clinical Advances
October 26, 2024 | Location: Room 4, Convention Center
Abstract Time: 05:00 PM - 05:10 PM
Category: Fluid, Electrolytes, and Acid-Base Disorders
- 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical
Authors
- Buchkremer, Florian, Kantonsspital Aarau AG, Aarau, Aargau, Switzerland
- Winzeler, Bettina, Universitatsspital Basel, Basel, BS, Switzerland
- Segerer, Stephan, Kantonsspital Aarau AG, Aarau, Aargau, Switzerland
- Christ-Crain, Mirjam, Universitatsspital Basel, Basel, BS, Switzerland
Background
Traditional algorithms of hypotonic hyponatremia use specific thresholds of volume status, urine sodium concentration (una), and urine osmolality (uosm) to identify its most relevant pathomechanism. In contrast, we hypothesized, that different etiologic factors occur together and that these thresholds do not reliably discriminate between them.
Methods
We used patient data (n=298) from a previous, prospective, observational study. We analyzed multiple etiologies of hypotonic hyponatremia (Figure) in subgroups defined by volume status (hypo-/eu-/hypervolemia), una (<= or > 30mmol/l), and uosm (<= or > 100mosm/kg). We quantified three primary etiologies (Figure), (1) high net free water intake (HNFWI), (2) impaired dilution of the urine (IDU), and (3) low nonelectrolyte solute excretion (LNESE), by projected, equivalent treatment effects, the ’standard delta sodium’ values (Buchkremer F et al., Kidney Int Rep. 2023).
Results
Prevalence and extent of all primary etiologies (Figure) showed only minor variations between hypo-, eu-, and hypervolemic patients. With una >30mmol/l, the impact of IDU was significantly higher than with una <=30mmol/l, while HNFWI and LNESE were similar in both groups. Uosm <=100mosm/kg did identify patients with very high levels of HNFWI. However, this group consisted of only 4 individuals, a mere 1.3% of the whole cohort, and less than 5% of those patients, where HNFWI had the highest quantitative impact of all primary etiologies.
As a remarkable result among the secondary etiologies, we found that factors associated with ’inappropriate antidiuresis’ (Figure) were present in 63.8% of all patients and that their prevalence was independent of volume status and una. Notably, two thirds of these patients showed additional secondary etiologies of IDU, that would preclude a traditional diagnosis of SIAD.
Conclusion
Current thresholds of volume status, urine sodium concentration, and urine osmolality provide only limited etiologic differentiation of hypotonic hyponatremia and do not reflect its mostly multifactorial etiology.