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Association between serum calcium and 28-day mortality in critically ill patients with COVID-19: A retrospective

Jianmin Qu¹, Yingxiu Huang², Lihua Shen³

¹Department of Intensive Care Unit, Tongxiang First People's Hospital, Tongxiang, Zhejiang Province, China.

|December 23, 2025

Insights

Higher serum calcium levels in critically ill coronavirus disease 2019 (COVID-19) patients are linked to lower 28-day mortality. This finding suggests serum calcium may aid in assessing prognosis and managing COVID-19 patients.

Area of Science:

Critical Care Medicine
Internal Medicine
Biochemistry

Background:

Serum calcium levels are vital prognostic indicators in critical illnesses.
The specific association between serum calcium and 28-day mortality in COVID-19 patients remains under-explored.
Understanding this relationship can inform patient management and prognosis assessment strategies.

Purpose of the Study:

To investigate the association between serum calcium concentrations and 28-day mortality in critically ill COVID-19 patients.
To determine if serum calcium levels at admission can predict mortality risk in this population.
To provide insights into the role of calcium in COVID-19 outcomes.

Main Methods:

Retrospective cohort analysis of 806 intensive care unit admitted COVID-19 patients from the MIMIC-IV database.
Data collection included vital signs, laboratory results, and pre-existing conditions.
Statistical analysis, including hazard ratios and confidence intervals, was used to assess the association between serum calcium and 28-day mortality, with adjustments for confounding factors.

Main Results:

The cohort exhibited a 28-day mortality rate of 27.7%.
Elevated serum calcium levels at admission were significantly associated with a lower 28-day mortality rate (HR=0.71, P<0.001).
This association persisted after adjusting for confounders (HR=0.83, P=0.021), with the highest calcium tertile showing reduced mortality risk (HR=0.70, P=0.043).

Conclusions:

Elevated serum calcium concentrations upon admission are independently associated with reduced 28-day mortality in critically ill COVID-19 patients.
Serum calcium levels may serve as a valuable biomarker for prognosis assessment in COVID-19 critical care.
Further research is warranted to explore the underlying mechanisms and clinical implications of this finding.

Read full analysis

Abstract:

Although serum calcium levels are associated with the prognosis of various critical illnesses, their specific relationship with 28-day mortality in critically ill patients with coronavirus disease 2019 (COVID-19) remains unclear. This relationship has potential implications for patient management and prognosis assessment. This investigation examines the association between serum calcium concentrations and 28-day mortality among severely ill patients with COVID-19. This retrospective cohort analysis encompassed 806 intensive care unit admitted COVID-19 patients, utilizing data extracted from the Medical Information Mart for Intensive Care - IV (MIMIC-IV) 3.0 database. Information regarding vital signs, laboratory test results, and preexisting conditions was compiled to explore the association of serum calcium concentrations with 28-day mortality. This study comprised 806 critically ill COVID-19 patients, averaging 64 years of age, of which 59% were male. The 28-day mortality rate for this cohort was 27.7%. Preliminary analyses indicated a strong relationship between elevated serum calcium levels at admission and a lower 28-day mortality rate (hazard ratio [HR] = 0.71; 95% confidence interval [CI] = 0.61-0.82; P < .001). Following adjustment for various confounding factors, the correlation between serum calcium concentrations and decreased 28-day mortality retained statistical association (HR = 0.83, 95% CI = 0.71-0.97, P = .021). Stratification of calcium concentrations into tertiles showed that patients in the top tertile (T3) exhibited a markedly decreased risk of 28-day mortality versus individuals within the bottom tertile (T1) (model III: HR = 0.70, 95% CI = 0.50-0.99, P = .043). Subgroup assessments showed comparable results across distinct demographic groups. Elevated serum calcium concentrations at the time of admission were linked to a reduced 28-day mortality in critically ill patients with COVID-19, offering a new perspective on the role of calcium in the management and prognosis of COVID-19.

Keywords:

COVID-19 MIMIC-IV calcium mortality

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