Twelve studies with 2,197 patients were included in the study. Through the initial database search, 718 studies were investigated for compliance with the inclusion criteria, of which 37 studies were ultimately chosen for consideration. Twenty-five studies were excluded from the meta-analysis for the following reasons: 1) 4 studies were descriptive and only reported biomarkers in all patients and did not compare critical/died versus not critical/alive patients. These studies did not define cardiac injury and did not assess OR for mortality with cardiac injury; 2) 19 studies did not report the biomarkers being studied; and 3) 2 studies reported biomarkers based on increased or normal D-dimers. Eleven studies were retrospective, and nine were single center (Table 1). Of the studies that reported time to blood sample collection, the average time reported was at the time of admission to 48 hours after admission. Of the studies that reported time to death or discharge, most of the studies reported it as the time from symptom onset to death or discharge. The average time for symptom onset to discharge was 27 days, and from symptom onset to death was 19 days. Two studies did not report median/mean cardiac biomarkers by predetermined patient groups,20, 21 but reported an OR for mortality based on cardiac injury. Five studies reported biomarkers based on whether the patients survived or died, 20, 22-25 five studies reported them based on whether the patient was critically ill or not. 11-14, 26 Of the latter studies, 4 categorized patients as sick based on the need for ICU admission, and 1 study based it on evidence of ARDS.21 Baseline demographics and comorbidities of patients included in the studies are shown in Table 2.
Troponin:
Nine studies with a total of 1,355 patients were included for this analysis. Five of the studies compared critically ill versus not critically ill patients, and the other 4 studies compared levels in dead versus alive patients. Results showed that patients who died or were critically ill had significantly higher troponin levels compared to patients who were alive or were not critically ill (WMD- 0.58, 95% CI 0.42-0.71, p<0.001). Sub-group analysis of the studies evaluating patients who died compared to patients who were alive showed that there was a significantly higher troponin level in those who died (WMD- 0.60, 95% CI 0.45-0.75, p<0.001). On the other hand, meta-analysis of studies comparing troponin levels in patients who were critically ill to those in patients who were not critically ill showed no difference in troponin levels (WMD- 0.28, 95% CI -0.14-0.69, p=0.19, Figure 2). The difference between these 2 groups of studies, i.e., studies that compared dead and alive and those that compared critically ill and not critically ill patients, was not significantly different (p-0.14).
The test for heterogeneity for the analysis of the 9 studies was an I2 of 58.5; therefore, a multivariate meta-regression analysis was performed with age, male gender, diabetes, hypertension, and cardiovascular disease. This analysis showed that hypertension (p=0.016, Supplemental Figure 2) and cardiovascular disease (p=0.001), (Supplemental Figure 3), contributed to the differences among studies in the reported troponin levels between the compared groups (R=1). Specifically, with increasing incidence of hypertension, there was a higher WMD in the troponin levels in patients who were dead or critically ill compared to levels in patients who were alive or not critically ill. The incidence of cardiovascular disease in the studies, on the other hand, was inversely related to the WMD of troponin between the groups.
Risk of death based on biomarker proven cardiac injury: We included 4 studies that reported a hazard ratio for death or event rates based on cardiac injury. Of these studies, 1 study used CK-MB without providing a definition.26 One study16 used troponin T and defined cardiac injury as troponin T levels above the 99th percentile upper reference limit. Troponin I levels were used in two studies, and both studies defined cardiac injury as troponin I levels above the 99th percentile upper reference limit. 21, 24
For the purpose of the meta-analysis, we extracted adjusted effect sizes, when available. In studies that did not report adjusted effect sizes, unadjusted OR was extracted. One study reported number of deaths and total sample size in each group, which was used in the analysis. Our analysis showed that cardiac injury was independently associated with significantly increased odds of mortality (OR- 6.641, 95% CI 1.26-35.1, p=0.03).
BNP:
There were 5 studies with 835 patients that reported NT-proBNP. Three studies compared critically ill versus not critically ill patients, and the other 2 studies compared results from dead and alive patients. Analysis of these 5 studies did not show a significant difference in BNP levels in patients who died or were critically ill compared to levels in those who were alive or were not critically ill (WMD-0.35, 95% CI -0.15-0.86, p=0.17). Similarly, sub-group analysis showed that there was no significant difference in patients who died compared to patients who were alive (WMD-0.37, 95% CI -1.01-1.74, p=0.60) and patients who were critically ill and those who were not (WMD 0.35, 95% CI -0.20-0.89, p=0.21). (Supplemental Figure 1)
Creatinine kinase (CK):
Seven studies with a total of 1,018 patients were included in this analysis. Four of the studies compared critically ill versus not critically ill patients, and the other 3 studies compared CK levels in dead patients versus alive patients. There was no significant difference in the CK levels in patients who died or were critically ill and those in patients who were alive or were not critically ill (WMD 0.20, 95% CI -0.03-0.44, p=0.88). Sub-group analysis showed that there was a significantly higher CK level in patients who died (WMD-0.47, 95% CI 0.09-0.84, p=0.014) compared to patients who survived, whereas the patients who were critically ill did not have significantly higher CK levels compared to the patients who were not critically ill (WMD-0.04, 95% CI -0.26-0.33, p=0.82). (Figure 3) The difference between these 2 groups of studies (studies comparing dead versus alive and those that compared critically ill versus not critically ill patients) was not significantly different.
D-dimer:
Six studies with a total of 957 patients evaluated D-dimer levels in COVID-19 patients. Four studies compared critically ill versus not critically ill patients, and the other two compared levels from dead patients versus alive patients. Analysis of these six studies showed that patients who died or were critically ill had significantly hiFgher D-dimer levels compared to patients who were alive or were not critically ill (WMD OR 0.54, 95% CI 0.4-0.68, p<0.001). Sub-group analysis of studies evaluating patients who died compared to patients who were alive showed that there was a significantly higher D-dimer level in those who died (WMD-0.51, 95% CI 0.30-0.71, p<0.001). Similarly, critically ill patients had a significantly higher D-dimer level compared to the patients who were not critically ill (WMD-0.57, 95% CI 0.38-0.76, p<0.001). (Supplemental Figure 4)
LDH:
Eight studies with a total of 1,219 patients evaluated LDH levels in COVID-19 patients. Five of the studies compared critically ill versus not critically ill patients, and the other three compared levels from dead patients versus alive patients. Analysis of these eight studies showed that patients who died or were critically ill had significantly higher LDH levels compared to patients who were alive or were not critically ill (WMD-0.55, 95% CI 0.38-0.73, p<0.001). Sub-group analysis showed that there was a trend towards a higher LDH level in those who died (WMD-0.98, 95% CI -0.08-2.04, p=0.07) compared to those who were alive, and that critically ill patients had significantly higher LDH levels compared to patients who were not critically ill (WMD-0.54, 95% CI 0.36-0.72, p<0.001). The difference between these two groups of studies, dead versus alive and studies that compared critically ill versus not critically ill patients, was not significantly different. (Supplemental Figure 5)