Iron and ferritin effects on intensive care unit mortality: A meta-analysis

Table 1 Characteristics of the studies included in the meta-analysis

Ref.	Population and country	Period	Study type	Age	Adjustment OR (95%CI)	ICU type	Patient types	NOS
Rimmelé et al[13]	1260, Italy	From February 22 to May 31, 2020	Cohort	Median age of 63 yr	Ferritin: 1.000 (1.000–1.000)	ICUs	COVID-19	7
Deng et al[14]	100, China	From January 30 to March 30 2020	Cohort	Median age of 65 yr	Ferritin: 32.63 (8.30–128.32)	ICUs	COVID-19	7
Lachmann et al[17]	116310, Germany	From January 2006 to August 2018	Cohort	18 years old or older	Ferritin: 1.518 (1.384–1.665)	Adult ICU	Critically ill patients	8
Tonial et al[15]	1407, Brazil	From July 2013 to January 2017	Cohort	6 months to 18 yr old	Ferritin: 5.17 (2.619-10.205)	Pediatric ICU	Sepsis	8
Brandtner et al[18]	61, Austria	From February 2018 to December 2019	Cohort	Mean age of 63 yr	Ferritin: 6 (1.1-39)	Adult ICU	Sepsis	7
					Iron: 4.6 (1.5-17)
Shu et al[16]	483, United States	From 2001 to 2012	Cohort	Aged 16 yr or above	Ferritin (90 D): 1.001 (1.000-1.001)	Adult ICU	AKI	6
					Iron (90 D): 1.741 (1.285-2.358)
Jiang et al[20]	258, China	From May 1 2016 to November 30 2017	Cohort	18 yr old or older	Ferritin: 1.010 (1.000–1.021)	Adult ICU	Sepsis	6
Xia et al[19]	250, China	From June 2015 to May 2017	Cohort	18 yr old or older	Iron: 0.696 (0.268-0.918)	Adult ICU	Critically ill patients	6
Lan et al[23]	1891, United States	From 2001 to 2012	Cohort	Aged 16 yr or above	Ferritin: 1.000 (0.999–1.000)	Adult ICU	Sepsis	6
					Iron: 1.506 (1.190–1.908)
Xie et al[21]	103, China	From August 2016 to January 2017	Cohort	18 yr old or older	Ferritin (long-term): 1.002 (1.000–1.003)	NCU	Neuro-critically patients	6
Lasocki et al[22]	2087, France	From August 2011 to June 2013	Cohort	Unlimited	Ferritin: 1.02 (0.51-2.06)	ICUs	Iron deficiency	7
Ghosh et al[24]	42, South Asia	From May 2016 to March 2017	Cohort	6 months to 12 yr old	Ferritin: 1.94 (0.94–4.02)	Pediatric ICU	Septic shock	6
Tacke et al[9]	312, Germany	Not provided	Cohort	Median age of 64 yr	Ferritin (long-term): 1.000 (1.000–1.000)	Adult ICU	Critically ill patients	7
					Iron (long-term): 1.040 (1.011–1.071)
Unal et al[26]	111, Turkey	Between May 2012 and January 2013	Cohort	Mean age of 73.79	Ferritin: 1.002 (1.000-1.004)	Adult ICU	Critically ill patients	6
Carcillo et al[29]	100, Pittsburgh	Not provided	Cohort	Age greater than or equal to 44 wk gestation and less than 18 yr	Ferritin: 1.001 (1.000–1.001)	Pediatric ICU	Sepsis	7
Uscinska et al[25]	392, Poland	Between 2008 and 2011	Cohort	Mean age of 70	Iron: 0.85 (0.78–0.94)	ICUs	Anemia	7
Leaf et al[8]	121, United States	Between 2008 and 2012	Cohort	Age >18 yr	Iron (long-term): 1.38 (0.91-2.10)	ICUs	AKI	6
Bennett et al[27]	171, United States	Between September 2, 2003, and August 16, 2007	Cohort	Age < 18 yr	Ferritin: 4.32 (2.21-8.47)	Pediatric ICU	Critically ill patients	6
Garcia et al[28]	31, Brazil	From January 2004 to September 2005	Cohort	Aged 1 month–16 yr	Ferritin: 3.2 (1.3-7.9)	Pediatric ICU	Sepsis	6

OR: Odds ratio; NOS: Newcastle-Ottawa scale; ICU: Intensive care unit; NCU: Neuro critical care unit; COVID-19: Coronavirus disease 2019; AKI: Acute kidney injury.

Table 2 Stratified analysis of iron parameters and mortality in critically ill patients according to study characteristics

Group	Number of the study	RR (95%CI)	P value	I2 (%)
Ferritin
Geographic region
Europe	6	1.001 (1.001-1.002)	< 0.01	94.3
America	5	1.002 (1.002-1.004)	0.293	19.1
Others	5	1.001 (1-1.001)	0.001	78.2
NOS
6	8	1.001 (1.001-1.001)	0.001	70.5
7	6	1.001 (1.001-1.001)	0.72	0
8	2	1.523 (1.383-1.663)	0.059	71.9
Patient types
Sepsis	7	1.001 (1.001-1.001)	0.004	68.2
Other critically ill patients	9	1.001 (1.001-1.002)	< 0.01	89.9
ICU types
Adult ICU	8	1.001 (1-1.001)	0	91.3
Pediatric ICU	5	1.001 (1.001-1.002)	0.017	66.9
General ICU	3	1.025 (0.25-1.8)	0.302	6.2
Iron
Geographic region
Europe	2	1.017 (0.988-1.045)	< 0.01	94.7
America	3	0.858 (0.573-1.143)	0.09	58.4
Others	2	1.616 (1.318-1.914)	0.583	0
NOS
6	4	1.217 (1.011-1.424)	0.001	82.7
7	3	1.017 (0.989-1.045)	< 0.01	89.9
Patient types
Sepsis	2	1.567 (1.208-1.925)	0.442	0
Other critically ill patients	5	1.017 (0.989-1.045)	< 0.01	87.2
ICU types
Adult ICU	5	1.043 (1.013-1.073)	0.001	79.7
General ICU	2	0.859 (0.780-0.939)	0.084	66.6

RR: Relative risk; NOS: Newcastle-Ottawa scale; ICU: Intensive care unit; I²: I-squared statistic.