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Human biomarkers for measuring iodine intake and status

Traditionally, iodine status was assessed by population goitre rate (16), however goitre is not sensitive to recent changes in iodine intakes and can be challenging to assess manually, particularly when small. Thyroid volume, measured by ultrasound, is often used clinically and can be an adjunct in research studies. Urinary iodine concentration (UIC) is the recommended biomarker of population iodine status (16). Thyroglobulin (Tg) measured in serum or whole blood on dried blood spots (DBS) has proved to be a sensitive and complementary biomarker of iodine status (4, 6, 7, 18, 19). Neonatal TSH may be used to assess iodine sufficiency in the population (16). Measurement of serum TSH and one or both thyroid hormones is routine in clinical settings to diagnose thyroid disorders, but thyroid function markers are usually within normal ranges in mild iodine deficiency and not recommended for monitoring iodine nutrition.


Table: Summary of biomarkers of iodine intake and status (adapted from (20)


Population assessment

Threshold for sufficiency

Thresholds for excess




Iodine status

In schoolchildren:
mUIC 100–299 mg/L

<20 % of sample population should have UIC<50 mg/L


In non-pregnant, adult women:
mUIC >100 mg/L


In pregnant women:
mUIC 150–249 mg/L

Population median:


≥300 mg/L in school children


≥500 mg/L in pregnant women


≥200 mg/L in populations with longstanding iodine deficiency with rapid increases in iodine intake

Reflects recent iodine intake

(16, 17)


Iodine status


Iodine intakes during
preceding ~month


Thyroid activity

Iodine-sufficient adults:
3-40 mg/L (a)



4-40 mg/L (b)

Pregnant women:
0.3-43.5 mg/L (c)

>3% of values >40 mg/L

Reference range may vary by specimen type, assay or population.

Some reports of confounding due to TgAb

(a) (20)

(b) (7, 19, 21)

(c) (6)


Iodine sufficiency

<5% TGR in sample population

Not established

Undertaken by palpation or ultrasound.

Inter-observer variation high.



Population risk of iodine deficiency (using neonatal TSH screening data)

In neonatal TSH screening programs:
<3% of values
>5 mlU/L


Reference range may vary by specimen type, assay or population.

Neonatal TSH data may reflect population risk of moderate to severe iodine deficiency during pregnancy.

May be confounded by use of iodine-containing antiseptics at birth.



Iodine status of lactating women



Recommended as adjunct to UIC in lactating women


BMIC: breast milk iodine concentration; DBS: dried blood spot; NA: not applicable; Tg: thyroglobulin; TgAb: thyroglobulin autoantibodies; TSH: thyroid stimulating hormone (thyrotropin); Tvol, Thyroid volume; UIC: urinary iodine concentration; mUIC: median UIC.