Hypophosphatemia predicts in-hospital acute kidney injury and mortality

Acute Kidney Injury (AKI), characterized by a high incidence rate and a poor prognosis, is believed to be associated with hyperphosphatemia. However, research on the impact of hypophosphatemia in this condition remains limited. This study aimed to assess the relationship between admission serum phosphate levels and the risks of in-hospital AKI and mortality. This large retrospective study enrolled hospitalized adult patients from January 2015 to December 2021 in Peking Union Medical College Hospital. We classified patients into seven groups based on their serum phosphate levels at admission. Then we analyzed the association between admission serum phosphate levels and the risks of in-hospital AKI and mortality, adjusting for confounders and performing sensitivity analysis. A total of 40,884 patients were enrolled in the study. The percentage of AKI was 26.2%, 17.4%, 15.6%, 14.9%, 15.2%,19.7%, and 40.9% in patients with admission serum phosphate levels < 0.81,0.81 to < 0.97,0.97 to < 1.13, 1.13 to < 1.29, 1.29 to < 1.45, 1.45 to < 1.78, and ≥ 1.78mmol/L, respectively. After adjusting for potential confounders, both hypophosphatemia and hyperphosphatemia were independently associated with the development of AKI. Only hypophosphatemia remained a consistently significant independent marker associated with in-hospital mortality. Compared with the normal admission serum phosphate category, hypophosphatemia independently associated with the risk of AKI and in-hospital mortality, especially in patients with eGFR of more than 60 ml/min/1.73m 2 and without concurrent kidney disease. To our knowledge, this large-scale study comprehensively demonstrated that hypophosphatemia at admission was statistically associated with the occurrence and outcomes of AKI, shedding light on the potential role of proximal tubule dysfunction as a novel pathophysiological mechanism.