• Yang Chen, Mengdi Luo, Huange Xu, Weiwei Zhao, and Qing He.
• Emergency, Affiliated Hospital of Southwest Jiaotong University / The Third People's Hospital of Chengdu, Chengdu, Sichuan, China.
• BMJ Open. 2021 Sep 6; 11 (9): e044473.

ObjectivesThis research aims to explore the impact of serum phosphate on the mortality of critically ill patients.DesignA retrospective large cohort study.SettingOur data were extracted from a publicly accessible database named 'Multiparameter Intelligent Monitoring in Intensive Care Database III'.Participants27 131 patients were included by clear definitions of selection and exclusion criteria.InterventionsWe used initial phosphate at admission as a design variable. Patients were divided into six groups with different serum phosphate levels and five groups at different intensive care unit (ICU) departments.Primary And Secondary Outcomes28-day and 90-day mortality were primary outcomes. All-cause mortality and length of stay ICU were secondary outcomes.ResultsPatients with very-high-normal serum phosphate, hypophosphataemia and hyperphosphataemia had worse outcomes. And the relationship between serum phosphate and the probability of 28-day or 90-day mortality had a linear relationship. After adjustment for potential confounders, hypophosphataemia and hyperphosphataemia were not significantly associated with 28-day or 90-day mortality. Nevertheless, at the medical ICU, hyperphosphataemia was associated with increased 28-day or 90-day mortality (HR=0.64, 95% CI 0.48 to 0.84, p=0.0017; HR=0.72, 95% CI 0.57 to 0.91, p=0.0067, respectively), using group 2 (≥2.5 mg/dL and <3.0 mg/dL) as the reference group.ConclusionsPatients with very-high-normal serum phosphate also had worse outcomes, it might be necessary to re-evaluate the definitions of the normal reference range for serum phosphate. Hypophosphataemia and hyperphosphataemia are not the independent risk factors of 28-day or 90-day ICU mortality, which leads us to consider whether phosphate monitoring is not a necessary measure in critically ill patients. But hyperphosphataemia was associated with increased 28-day or 90-day mortality at the medical ICU, which emphasises the potential importance of early diagnosis and treatment of hyperphosphataemia for the patients who were admitted to the medical ICU.© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

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