LAB MANAGEMENT :: HYPONATREMIA OUTCOMES unchanged.41


More recently, globally rec-


ognized expert panels in the United States and Europe have published evidence- based guidelines discussing the critical role that serum and urine osmolality mea- surements play in the classification and differential diagnosis of hyponatremia.1,7,42 The utility of osmolality has also been recognized in the management of COVID patients due to the prevalence of hyponatremia in this patient popu- lation.43,44,45


O’Shea et al. published a


COVID test menu for clinical laboratories that includes osmolality testing due to the potential for acute kidney injury in these patients. Similarly, Martinez et al. published guidance recommending daily monitoring of osmolality for inpatients during the acute phase of COVID-19.


Osmolality testing for proper patient management Osmolality is a proven and medically necessary test in the management of hypontremia. Failure to measure plasma and urine osmolality in cases of hypontre- mia has been associated with increased mortality.45,46


In a retrospective study of


adult patients with severe hyponatremia, Whyte et al. reported that 30% of patients died when neither serum nor urine os- molality was measured compared to 9.8% when both tests were measured.45 Similarly, Vaduganathan et al. analyzed serum osmolality measured at discharge in 3,744 patients hospitalized for heart failure and concluded that low discharge serum osmolality was independently predictive of worse discharge mortality and readmission.46 Knowledge and interpretation of a


patient’s osmolality in cases of hyponatre- mia enable the physician to differentiate between the various causes of the elec- trolyte disorder and appropriately direct treatment. This is a critical issue because treatment varies drastically based on symptoms and underlying causes. Hypo- natremia is treated with fluid restriction (in the setting of euvolemia), isotonic saline (in hypovolemia), and diuresis (in hypervolemia).47


Lack of osmolality


testing makes diagnostic accuracy and subsequent treatment uncertain putting hyponatremic patients at risk.


Underutilization of osmolality impedes management of hyponatremia


Despite published guidance on its diag- nosis, clear associations with poor out- comes and increased medical costs, and significant evidence that correcting hypo- natremia is associated with improved out-


3 DECEMBER 2022 MLO-ONLINE.COM 8 Hospital Clinician Laboratory


comes and lower costs, hyponatremia is insufficiently investigated or overlooked entirely, and critical testing is not routine impacting patient treatment.36,48,49,50 Inadequate requisition of serum and urine osmolality is frequent in cases of hyponatremia. In a multicenter, retro- spective, observational study, Tzoulis et al. found that only 23% of patients with hy- ponatremia had measurements of paired serum and urine osmolality and sodium.50 The study from Tzoulis et al. is not an outlier; numerous publications in the literature have consistently reported un- derutilization of measured osmolality in the investigation of hyponatremia.29,35,51,52,53 Huda et al. evaluated the assessment and management of hyponatremia in a large teaching hospital and found that adequate investigations were rarely performed. In fact, plasma osmolality was measured in only 26% of patients with severe hyponatremia and urine osmolality was measured in only 27%. The authors observed that treatment was often illogical with significant man- agement errors in 33% of cases. Errors included, but were not limited to, inad- equate investigation which could have changed management, treatment with fluid restriction plus intravenous saline, and diuretic induced hyponatremia treated with fluid restriction. Further, mortality was significantly higher in the group with management errors (41% versus 20%). The authors suggest that more appropriate management may have reduced the overall mortality rate. Additionally, they found a trend towards more efficient normalization of serum sodium concentrations in the appropriately managed group, deemed appropriate based on standards for the major diagnostic criteria of hyponatre- mia.51


Seo et al. reported similar manage- ment errors as Huda et al. The authors


Stakeholder Patient


Benefits


• Improved outcomes (i.e., better prognosis, reduced length of stay) • More effective treatment


• Improvement in readmission rate and reduced associated penalty59 • Increased profit from reduction in costs • Differentiation from other hospitals via better patient experience


• Evidence-based decision-making tool to improve patient care • Improved patient outcomes


• Increased efficiencies • Expedited patient care


Figure 3. Osmolality testing: Key stakeholders and benefits.


highlighted the importance of osmolality test results in guiding therapy.47 Even SIADH, the most common cause of


hyponatremia, is often diagnosed without attention to the accepted diagnostic cri- teria.7,29,52,53


Greenberg et al. conducted


an analysis of adult patients in the Hy- ponatremia Registry from 225 sites in the United States and European Union and observed that only 47% of 1,524 patients with an assigned diagnosis of SIADH had all three cardinal tests (serum osmolal- ity, urine osmolality, and serum sodium) performed and 11% had none. Serum os- molality was measured in 66% of patients and urine osmolality in 68%.52


Burst et al.


studied smaller subsets of the Hypona- tremia Registry. The authors analyzed 358 cancer patients with a clinical diagnosis of SIADH and similarly found that only 46% of patients had all three tests per- formed, and 13% had none. They reported that test underutilization was even more pronounced in subgroups including lung cancer patients and small cell lung cancer patients with all tests performed in only 41% and 36% of patients respectively.53 Diagnostic rigor appears to be even


worse in COVID patients. In a retrospec- tive, multicenter, observational cohort study of hospitalized patients with labo- ratory-confirmed SARS-CoV-2, Frontera et al. attempted to determine the etiology of hyponatremia but were unsuccessful because serum and urine osmolality were available in less than 15% of the cohort.29 Yen et al. reported that serum and urine osmolality measurements were avail- able as part of admission hyponatremia workup tests in only 18% and 12% of cases respectively. Further, the authors reported that serum and urine osmolality were only ordered on the day of admission, when hyponatremia was identified, in 9% and 5.4% of cases respectively.54


Similarly, Car- valho et al. reported that osmolality was


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