Table 4.

Observational Studies Measuring Tg in Relation to Iodine Status in Newborns, Children, and Adults

Authors	Age (years)a; nb; country	UICc (μg/L)			Tgc (μg/L)			Findings	Comments
Newborns
Andersen et al. (37)	Newborns; n=140; Denmark	No supplements		—	No supplements		61.6d	Infants of mothers taking iodine supplements of 150 μg I/day had a significantly lower Tg than infants born to mothers not taking supplements (p<0.001)	A lag period (i.e., 5 days) between the collection of urine from infant and cord blood samples
		Supplements		—	Supplements		31.1d
		All		44d	All		50.0d
Children
Simsek et al. (39)	8–10; n=727; Turkey	Urbane			Urbane			Severely iodine deficient children had a significantly lower Tg than children with mild to moderate iodine deficiency and iodine sufficient children (p<0.001); Tg was negatively correlated with urinary iodine (r=− 0.27, p<0.001).
		Düzce		96	Düzce		10.9
		Bolu		108	Bolu		8.4
		Rural			Rural
		Yiğilca		13	Yiğilca		59.1
		Mudurnu		46	Mudurnu		27.2
		Akçakoca		71	Akçakoca		14.2
		Gerede		75	Gerede		12.8
Zimmermann et al. (40)	5–14; n=710; 5 countries	Countries:			Countries:			Purpose of this study was to determine the Tg reference interval of children (i.e., 4–40 μg/L). Of the five countries, children from three countries had high Tg despite being iodine sufficient
		Bahrain		177	Bahrain		19.3
		Peru		161	Peru		11.6
		South Africa		266	South Africa		18.4
		China		234	China		13.3
		Switzerland		130	Switzerland		11.2
		All		198	All		14.5
Bayram et al. (30)	10–14; n=109; Turkey	51e			49.9e			Nongoitrous children had a significantly lower Tg than goitrous children (p<0.001); Tg was negatively correlated with urinary iodine (r=− 0.611, p<0.05)
Skeaff et al. (73)	5–14; n=1153; New Zealand	Age (years)			Age (years)			Iodine sufficient children had a significantly lower Tg than iodine deficient children (p<0.001)
		5–7		63	5–7		16.2
		8–10		67	8–10		12.5
		11–14		75	11–14		11.1
		All		68	All		12.9
Skeaff and Lonsdale-Cooper (55)	8–10; n=147; New Zealand	113			10.8			UIC indicated adequate iodine status but Tg indicated mild iodine deficiency, suggesting that the children still had thyroid enlargement	Correction factor of 0.588 used to adjust for intraassay variation in Tg values between ECLIA and RIA method
Zimmermann et al. (41)	6–12; n=2512; 12 countries	Countries:			Countriesd:			Tg followed a U-shaped curve from severely deficient to excessive iodine intake as assessed by UIC
		Morocco		16	Morocco		25.5
		Tajikistan		52	Tajikistan		10.9
		Switzerland		137	Switzerland		10.5
		Philippines		154	Philippines		13.1
		Bahrain		178	Bahrain		18.0
		Peru		197	Peru		11.5
		Croatia		205	Croatia		11.3
		China		235	China		12.6
		Indonesia		235	Indonesia		9.8
		Paraguay		257	Paraguay		13.6
		South Africa		282	South Africa		18.6
		Tanzania		338	Tanzania		17.6
		All		151	All		13.3
Adults
Fenzi et al. (25)	38.8; n=840; Italy	Endemic goiter		44e,f	Endemic goiter		49.9e	Adults living in an iodine sufficient area had a significantly lower Tg than adults living in an endemic goiter area (p<0.01); Tg was negatively correlated with urinary iodine (r=− 0.185, p=0.001)
		Iodine sufficient		88e,f	Iodine sufficient		9.5e
Gutekunst et al. (45)	≥17; n=1291; Germany and Sweden	Germany		63g	Germany		43.0	German adults had a significantly lower Tg than Swedish adults (p<0.0001)
		Sweden		141g	Sweden		21.2
Pedersen et al. (38)	22–37; n=20; Denmark	42g			32.5				Six adults were positive for TgAb but were not included in Tg results
Hintze et al. (90)	60–97; n=286; Germany	64g			8.9			Adults with no goiter had a significantly lower median Tg than adults with goiter (p<0.001)
Laurberg et al. (46)	66–70; n=523; Denmark and Iceland	Denmark		38	Denmark		15.5	In Denmark (Jutland), 14.2% adults living had Tg >50 μg/L; while in Iceland, 3.4% adults had Tg >50 μg/L	Differences in Tg between adults living Denmark and Iceland not reported
		Iceland		150	Iceland		9.5
Knudsen et al. (44)	18–65; n=3759; Denmark	Copenhagen		68	Copenhagen		11.3	Adults living in Copenhagen had a significantly lower Tg than adults living in Aalborg (p<0.001)	Adults included those who were taking iodine supplements.
		Aalborg		53	Aalborg		15.2
Thomson et al. (91)	18–49; n=233; New Zealand	54			5.1			Tg was negatively correlated with UIC (r=− 0.210, p=0.003)
Rasmussen et al. (43)	18–65; n=4649; Denmark	Copenhagen		68	Copenhagen		11.5	Adults living in Copenhagen had a significantly lower Tg than adults living in Aalborg (p<0.001); Tg was negatively correlated with iodine intake	Adults included pregnant women (1.3%) and lactating women (1.8%)
		Aalborg		53	Aalborg		15.4
Teng et al. (42)	14–95; n=3761; China		Baseline	5 years		Baseline	5 years	Adults living in Zhangwu city had a significantly lower Tg than adults living in Huanghua and Pangshan cities at baseline (p<0.001) and 5 years (p<0.001)
		Panshan	103	97	Panshan	7.7	11.7
		Zhangwu	375	350	Zhangwu	6.0	9.1
		Huanghua	615	635	Huanghua	6.4	10.2
Bayram et al. (30)	28.7; n=109; Turkey	31e			68.9e			Adults with no goiter had a significantly lower Tg than adults with goiter (p<0.001)
Vejbjerg et al. (21)	18–65; n=4649; Denmark		IS			IS		Adults living in Copenhagen and Aalborg had a significantly lower Tg after introduction of mandatory iodization of salt (p<0.001)	This study included two cross-sectional samples
			Before	After		Before	After
		Copenhagen	61	99	Copenhagen	11.5	9.1
		Aalborg	45	86	Aalborg	15.4	9.3
Cahoon et al. (72)	10–33; n=7890; Belarus	NR			UIC (μg/L)			Adults with UIC 100–2120 μg/L had a significantly lower median Tg than subjects with UIC of 50–100, 20–50, and 0–20 μg/L (p<0.001)
					0–20		12.1
					20–50		9.7
					50–100		8.0
					100–2120		6.6

^aRange used unless mean reported.

^bOnly subjects with no known thyroid disease or negative for TgAb.

^cMedian used unless mean or geometric mean reported.

^dGeometric mean.

^eMean.

^fUIC reported as urinary iodine excretion (μg/day).

^gUIC reported as μg/g creatinine.