Admission serum phosphate levels predict hospital mortality

BACKGROUND: The aim of this study was to assess the relationship between admission serum phosphate levels and in-hospital mortality in all hospitalized patients. METHODS: All adult hospitalized patients who had admission serum phosphate available between years 2009 and 2013 were enrolled. Admission serum phosphate was categorized based on its distribution into six groups (<2.5, 2.5-3.0, 3.1-3.6, 3.7-4.2, 4.3-4.8 and ≥4.9 mg/dL). The odds ratio (OR) of in-hospital mortality by admission serum phosphate, using the phosphate category of 3.1-3.6 mg/dL as the reference group, was obtained by logistic regression analysis. RESULTS: 42,336 patients were studied. The lowest incidence of in-hospital mortality was associated with a serum phosphate within 3.1-4.2 mg/dL. A U-shaped curve emerged demonstrating higher in-hospital mortality associated with both serum phosphate <3.1 and >4.2 mg/dL. After adjusting for potential confounders, both serum phosphate <2.5 and >4.2 mg/dL were associated with in-hospital mortality with ORs of 1.60 (95%CI 1.25-2.05), 1.60 (95%CI 1.29-1.97), and 3.89 (95%CI 3.20-4.74) when serum phosphate were <2.5, 4.3-4.8 and ≥4.9 mg/dL, respectively. Among subgroups of patients with chronic kidney disease (CKD) and cardiovascular disease (CVD), the highest mortality was associated with a serum phosphate ≥4.9 mg/dL with ORs of 4.11 (95%CI 3.16-5.39) in CKD patients and 5.11 (95%CI 3.33-7.95) in CVD patients. CONCLUSION: Hospitalized patients with admission serum phosphate <2.5 and >4.2 mg/dL are associated with an increased risk of in-hospital mortality. The highest mortality risk is associated with CKD and CVD patients with admission hyperphosphatemia.