Impact of serum phosphate changes on in-hospital mortality

Fluctuations in serum phosphate levels increased mortality in end-stage renal disease patients. However, the impacts of serum phosphate changes in hospitalized patients remain unclear. This study aimed to test the hypothesis that serum phosphate changes during hospitalization were associated with in-hospital mortality.

We included all adult hospitalized patients from January 2009 to December 2013 that had at least two serum phosphate measurements during their hospitalization. We categorized in-hospital serum phosphate changes, defined as the absolute difference between the maximum and minimum serum phosphate, into 5 groups: 0-0.6, 0.7-1.3, 1.4-2.0, 2.1-2.7, ≥2.8 mg/dL. Using serum phosphate change group of 0-0.6 mg/dL as the reference group, the adjusted odds ratio of in-hospital mortality for various serum phosphate change groups was obtained by multivariable logistic regression analysis.

A total of 28,149 patients were studied. The in-hospital mortality in patients with serum phosphate changes of 0-0.6, 0.7-1.3, 1.4-2.0, 2.1-2.7, ≥2.8 mg/dL was 1.5, 2.0, 3.1, 4.4, and 10.7%, respectively (p < 0.001). When adjusted for confounding factors, larger serum phosphate changes were associated with progressively increased in-hospital mortality with odds ratios of 1.35 (95% 1.04-1.74) in 0.7-1.3 mg/dL, 1.98 (95% CI 1.53-2.55) in 1.4-2.0 mg/dL, 2.68 (95% CI 2.07-3.48) in 2.1-2.7 mg/dL, and 5.04 (95% CI 3.94-6.45) in ≥2.8 mg/dL compared to serum phosphate change group of 0-0.6 mg/dL. A similar result was noted when we further adjusted for either the admission or mean serum phosphate during hospitalization.

Greater serum phosphate changes were progressively associated with increased in-hospital mortality.