LAB MANAGEMENT :: HYPONATREMIA OUTCOMES
Figure 2. Clinical pathway for diagnosing hyponatremia.
monly observed clinical conditions, such as myocardial infarction, heart failure, cir- rhosis, and pulmonary infections. Waikar et al. investigated in-hospital, 1-year and 5-year mortality in a prospective cohort study of 98,411 hospitalized adults and found that patients with hyponatremia had an increased risk of death in-hospital at 1 year (47%) and 5 years (25%). The increased risk of death was evident even in those with mild hyponatremia (37%) and was pronounced in patients admitted with cardiovascular disease, metastatic cancer, and those admitted for procedures related to the musculoskeletal system.2 Poor outcomes have also been reported
in COVID patients with hyponatremia of varying severity levels.28,35
In a retrospec-
tive, multicenter, observational cohort study, Frontera et al. identified the impact of mild, moderate, and severe admission hyponatremia on outcomes among COVID patients and reported that each level of worsening hyponatremia conferred 43% increased odds of in-hospital death. Further, the authors observed that hypo- natremia was an independent predictor of
in-hospital mortality and was associated with increased risk of encephalopathy and mechanical ventilation. Similarly, Carvalho et al. conducted a retrospective study of 296 adult patients with a diagno- sis of COVID-19 and reported that ICU admission, mechanical ventilation, and death were significantly more frequent in hyponatremic patients compared to normonatremic patients (37% versus 14%; 17% versus 6%; 18% versus 9%).
Osmolality is well-established in the clinical pathway for hyponatremia Correction of hyponatremia first re- quires proper diagnosis. The common electrolyte disorder is classified as hypoosmolar, isoosmolar, or hyperos- molar. Understanding the underlying cause of hyponatremia is important as the treatment options vary widely from fluid resuscitation for hyponatremia driven by volume depletion to volume restriction for hyponatremia driven by the syndrome of inappropriate antidi- uretic hormone secretion (SIADH).37,38
It is important to cast a wide net in the initial workup of hyponatremia because patients may present with minimal in- formation regarding relevant medical conditions or recent triggering events.39 Interpreting various laboratory parame- ters, including serum and urine osmolal- ity, is necessary to differentiate between the various causes of hyponatremia and ensure proper patient management.40 Criteria for diagnosing hyponatremia is well-established.1,7,41,42
Measurement of
serum osmolality is the first step in the laboratory diagnosis of hyponatremia, and if the test suggests a hypo-osmolar state, then urine osmolality helps deter- mine whether the ability of the kidneys to dilute urine is intact (Figure 2).39 SIADH is the most frequent cause of
hyponatremia and the use of serum and urine osmolality to distinguish SIADH from other etiologies is critical. In 1967, Bartter and Schwartz originally defined the diagnostic criteria for SIADH, which include measuring serum osmolality, urine osmolality, and serum sodium at a minimum. Their criteria has remained
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