Admission hyperphosphatemia increases the risk of acute kidney injury in hospitalized patients

Abstract

Background: Evidence on the association between elevated admission serum phosphate and risk of in-hospital acute kidney injury (AKI) is limited. The aim of this study was to assess the risk of AKI in hospitalized patients stratified by admission serum phosphate level.

Methods: This is a single-center retrospective study conducted at a tertiary referral hospital. All hospitalized adult patients who had admission phosphate measurement available between January and December 2013 were enrolled. Admission phosphate was categorized into 6 groups (< 2.4, 2.4-2.9, 2.9-3.4, 3.4-3.9, 3.9-4.4, and ≥ 4.4 mg/dl). The primary outcome was in-hospital AKI occurring after hospital admission. Logistic regression analysis was performed to obtain the odds ratio of AKI for various admission phosphate strata using the phosphate 2.4-2.9 mg/dl level (lowest incidence of AKI) as the reference group.

Results: After excluding patients with end-stage renal disease (ESRD), without serum phosphate measurement, and those with AKI at time of admission, a total of 5036 patients were studied. Phosphate levels of < 2.4 and ≥ 4.4 mg/dl were found in 458 (9.1%) and 585 (11.6%) patients, respectively. In-hospital AKI occurred in 595 (11.8%) patients. The incidence of AKI among patients with admission phosphate < 2.4, 2.4-2.9, 2.9-3.4, 3.4-3.9, 3.9-4.4, and ≥ 4.4 mg/dl was 10.5, 9.5, 11.8, 10.0, 12.8, and 17.9%, respectively. After adjusting for potential confounders, admission serum phosphate > 4.4 mg/dl was associated with an increased risk of developing AKI with an odds ratio of 1.72 (95% confidence interval 1.20-2.47), whereas admission serum phosphate levels < 4.4 mg/dl were not associated with development of AKI during hospitalization.

Conclusion: Elevated admission phosphate is associated with an increased risk for in-hospital AKI.

Keywords: Acute kidney injury; Hyperphosphatemia; Hypophosphatemia; Phosphate.