Electrolyte abnormalities and severity, mortality, and resource utilization in U.S. cancer hospitalizations: National Inpatient Sample, 2018–2022.

e23190 Background: Electrolyte abnormalities are common during cancer hospitalizations and are often managed as isolated disturbances. National data describing their association with inpatient physiologic severity, mortality, and resource utilization in oncology hospitalizations remain limited. Methods: A serial cross-sectional, hospitalization-level analysis of the 2018 to 2022 Healthcare Cost and Utilization Project National Inpatient Sample (NIS) was performed using discharge-level survey weighting with hospital clustering and stratification to generate nationally representative estimates. Adult hospitalizations with a principal diagnosis of malignancy were identified using ICD-10-CM codes C00 to C97 and D45 to D47. ICD-defined electrolyte abnormality phenotypes included hyponatremia (E87.1), hypercalcemia (E83.52), hypokalemia (E87.6), and hyperkalemia (E87.5), with a composite exposure capturing any electrolyte abnormality. Primary outcomes were All Patient Refined Diagnosis Related Group (APR-DRG) severity of illness subclass, with extreme inpatient severity defined as APR-DRG level 4. Secondary outcomes included in-hospital mortality, length of stay (LOS), and hospitalization cost. Survey-weighted multivariable models adjusted for demographics, payer, socioeconomic status, admission characteristics, cancer type, and hospital characteristics. Results: Among 961,848 unweighted cancer hospitalizations representing 4,809,239 hospitalizations nationally, any electrolyte abnormality occurred in 24.07%. Hyponatremia occurred in 11.12%, hypercalcemia in 2.85%, hypokalemia in 10.97%, and hyperkalemia in 4.13%. Hospitalizations with any electrolyte abnormality had higher mean APR-DRG severity than those without (3.13 vs 2.40), longer LOS (9.79 vs 5.77 days), and higher mean cost ($28,812 vs $21,146). Extreme inpatient severity occurred more frequently in hospitalizations with electrolyte abnormalities than without (5.88% vs. 2.69%). After adjustment, any electrolyte abnormality remained independently associated with higher inpatient severity (beta 0.51, 95% CI 0.50-0.52), increased odds of extreme severity (OR 2.37, 95% CI 2.29-2.45), and higher mortality (OR 1.91, 95% CI 1.86-1.96). Hyperkalemia showed the strongest associations with inpatient severity (beta 0.59, 95% CI 0.56-0.62), extreme severity (OR 3.01, 95% CI 2.79-3.25), and mortality (OR 3.29, 95% CI 3.02-3.58). Conclusions: Electrolyte abnormality phenotypes are common in U.S. cancer hospitalizations and are independently associated with substantially higher inpatient physiologic severity, mortality, and resource utilization. These findings support electrolyte abnormalities as markers of inpatient vulnerability that may inform risk stratification and operational planning in hospitalized oncology populations.