Table 3. Data of copper between sickle cell disease patient(s) and non–sickle cell disease patient(s).

Study	Location	Design	Sickle cell disease patient(s)			Non–sickle cell disease patient(s)
			Mean	SD	n	Mean.c	SD	n
Akinkugbe and Ette (1987) 37	Africa	Cross-sectional	70.40	42.62	40	89.30	61.30	20
Alayash et al (1987) 49	Asia	Cross-sectional	144.93	44.09	57	148.40	44.40	45
Al-Naama et al, (2016) 51	Asia	Cross-sectional	145.50	14.30	42	100.90	13.50	50
Antwi-Boasiako et al, 2019	Africa	Cross-sectional	220.90	27.80	34	114.00	16.30	50
Bashir (1995) 55	Asia	Cross-sectional	131.30	11.50	15	109.00	15.10	25
Canellas et al (2012) 43	The United States	Cross-sectional	120.00	10.00	43	100.00	10.00	60
Emokpae et al (2019) 59	Africa	Case control	105.80	2.46	74	102.60	1.59	50
Erhabor et al (2019) 60	Africa	Case control	40.40	9.66	45	75.60	6.50	25
Hasanato et al (2019) 9	Asia	Cross-sectional	131.67	15.56	33	88.00	10.50	33
kehinde et al (2011) 25	Africa	Cross-sectional	6.00	2.00	20	7.00	3.00	20
Kilinç et al (1991) 28	Europe	Case control	133.80	64.67	20	168.70	39.30	20
Mukuku et al (2018) 33	Africa	Case control	172.00	15.00	76	189.00	20.00	76
Olaniyi et al (2010) 36	Africa	Case control	67.00	10.10	59	68.50	10.00	35
Oztas et al (2012) 40	Europe	Case control	95.90	9.90	15	96.30	9.10	10
Prasad et al, 1976	The United States	Case control	126.00	25.00	41	116.00	19.00	60
Smith et al (2019) 42	Africa	Cross-sectional	144.00	17.09	80	116.00	27.70	80
Yousif et al (2018) 45	Asia	Case control	142.35	49.92	87	109.66	24.42	90