Association of Serum Phosphate Derangement With Mortality in Patients on Continuous Renal Replacement Therapy

BACKGROUND: There is limited evidence on the association of serum phosphate with mortality in patients receiving continuous renal replacement therapy (CRRT). OBJECTIVE: To assess the association of serum phosphate with mortality in critically ill patients requiring CRRT for acute kidney injury (AKI). DESIGN: A cohort study. SETTING: A tertiary referral hospital in the United States. PATIENTS: Acute kidney injury patients receiving CRRT from 2006 through 2015 in intensive care units. MEASUREMENTS: (1) Serum phosphate before CRRT and (2) mean serum phosphate during CRRT were categorized into 3 groups; ≤2.4 (hypophosphatemia), 2.5 to 4.5 (normal serum phosphate group), and ≥4.6 (hyperphosphatemia) mg/dL. METHODS: Multivariable logistic regression was used to assess the association between serum phosphate and 90-day mortality. RESULTS: A total of 1108 patients were included in this study. Of these, 55% died within 90 days after CRRT initiation. Before CRRT, 3%, 30%, and 66% had hypophosphatemia, normophosphatemia, and hyperphosphatemia, respectively. Before CRRT, both hypophosphatemia and hyperphosphatemia were significantly associated with higher 90-day mortality with the adjusted odds ratio (OR) of 2.22 (95% confidence interval [CI]: [1.03, 4.78]) and 1.62 (95% CI: [1.21, 2.18]), respectively. During CRRT, 3%, 85%, and 12% had mean serum phosphate in hypophosphatemia, normophosphatemia, and hyperphosphatemia range. During CRRT, hyperphosphatemia was significantly associated with higher 90-day mortality with adjusted OR of 2.22 (95% CI: [1.45, 3.38]). LIMITATIONS: Single center, observational design, lack of information regarding causes of serum phosphate derangement. CONCLUSION: Most CRRT patients had hyperphosphatemia before CRRT initiation but maintain normal serum phosphate during CRRT. Before CRRT, hypo- and hyperphosphatemia, and during CRRT, hyperphosphatemia predicted higher mortality. TRIAL REGISTRATION: Not registered.