TABLE 1.

Characteristics of studies

SN	Author, Year	Type of study, centre	Country	Total no. of patients	Outcome
1.	Wang Y et al., 2020 33	Retrospective, SC	China	344	Non survivors had a higher RDW in comparison to the surviving COVID‐19 patients (p < 0.001).
2.	Foy et al., 2020 34	Retrospective, MC	USA	1,641	The mortality rate of COVID‐19 patients with RDW ≥14.5 at admission was higher (31%) in comparison to those with an RDW <14.5 (11%).
3.	Levy et al., 2020 35	Retrospective, MC	USA	11,095	High RDW value was associated with disease severity, progression and an overall poor prognosis
4.	Santos‐Lozano et al., 2020 36	Retrospective, SC	Spain	1,369	High RDW associated with risk of in hospital death in persons with COVID‐19
5.	Nicholson et al., 2020 37	Retrospective, MC	USA	1,042	Non survivors had a high level of RDW (14.84) in comparison to survivors (13.9) at admission.
6.	Rizo‐Téllez et al., 2020 38	Retrospective, SC	Mexico	54	No significant differences between survivors and non‐survivors were found for most of the haematological parameters
7.	Allahverdiyev et al., 2020 39	Retrospective, SC	Turkey	455	The mortality rate of COVID‐19 positively correlated with higher neutrophil‐to‐lymphocyte ratio, RDW
8.	Wei Y et al., 2020 40	Retrospective, SC	China	112	Mortality is associated with higher variation of RDW (HR, 2.63; 95%CI, 1.10‐6.30; p = 0.0297)
9.	Lorente et al., 2020 41	Prospective, MC	Spain	143	The deceased patients had a higher RDW (p = 0.001) in compare to surviving patients.
10.	Wang c et al., 2020 42	Retrospective, MC	China	98	RDW is a prognostic predictor for patients with severe COVID‐19
11.	Henry et al., 2020 43	Prospective, SC	USA	49	Progressive increase in RDW was associated with advancing COVID‐19 severity
12.	Gong et al., 2020 44	Retrospective, MC	China	189	Higher red blood cell distribution width was associated with severe COVID‐19.
13.	Jans et al., 2020 45	Retrospective, SC	Netherlands	254	Patients with severe disease had a higher RDW on admission.
14.	Wang C et al., 2020 46	Retrospective, SC	China	161	NLR and RDW‐SD parameter helps to predict the severity of COVID‐19 patients.
15.	Gowda et al., 2020 47	Retrospective, SC	India	100	RDW is an early predictive marker of mortality in COVID‐19
16.	Kaufmann et al., 2020 48	Retrospective, SC	Austria	423	Raised RDW was an important predictor of 28 days mortality [crude odds ratio (OR) 1.717, 95% confidence interval (CI) 1.462–2.017; P = <0.001]
17.	Paliogiannis et al., 2020 49	Case series, SC	Italy	30	Increased RDW associated with mortality
18.	Sema Yağc et al., 2020 50	Cross‐sectional, SC	Turkey	59	Elevated RDW in COVID‐19 patients had a higher rate of in‐hospital mortality*
19.	Tocoglu et al., 2020 51	Retrospective, SC	Turkey	55	In critically ill COVID‐19 patients with AKI low RDW may be associated with mortality.
20.	Soni et al., 2020 52	Retrospective, SC	India	622	Non survivors had a high level of RDW (15.45) in comparison to survivors (14.49) at admission.
21.	Ramchandran et al., 2020 53	Retrospective, SC	USA	294	COVID‐19 patients with elevated RDW value had a higher frequency of in‐hospital mortality
22.	De La Rica R et al., 2020 54	Case series, SC	Spain	48	No significant differences between survivors and non‐survivors were found for RDW
23.	Lin S et al., 2020 55	Retrospective, SC	China	68	No significant differences in haematological parameters between patients with mild and severe illness at the time of admission,
24.	Solmaz et al., 2020 56	Retrospective, SC	Turkey	1,950	Majority of the COVID‐19 patients with elevated RDW on admission required ICU care.
25.	Asan et al., 2020 57	Retrospective, SC	Turkey	695	Initial elevated RDW was associated with the severity of COVID‐19 and ICU requirement.

Abbreviations: AKI, Acute kidney injury; CI, confidence interval; COVID‐19, Coronavirus Disease 2019; MC, Multi centre; OR, odds ratio; RDW, Red blood cell distribution width; RDW‐SD, Red blood cell distribution width standard deviation; SC, Single centre.