Dried Blood Spot Thyroglobulin as a Biomarker of Iodine Status in Pregnant Women

Abstract

Context: Thyroglobulin (Tg) could be a sensitive biomarker of iodine nutrition in pregnant women (PW). A dried blood spot (DBS) assay would simplify collection and transport in field studies. Objectives: Our aims were to (1) establish and test a reference range for DBS-Tg in PW; (2) determine whether co-measurement of Tg antibodies (Abs) is necessary to define population iodine status. Design, Setting, and Participants: Standardized cross-sectional studies of 3870 PW from 11 countries. For the DBS-Tg reference range, we included TgAb-negative PW (n = 599) from 3 countries with sufficient iodine intake. Main Outcome Measures: We measured the urinary iodine concentration and DBS thyroidstimulating hormone, total thyroxin, Tg, and TgAb. Results: In the reference population, the median DBS-Tg was 9.2 g/L (95% confidence interval, 8.7 to 9.8 g/L) and was not significantly different among trimesters. The reference range was 0.3 to 43.5 g/L. Over a range of iodine intake, the Tg concentrations were U-shaped. Within countries, the median DBS-Tg and the presence of elevated DBS-Tg did not differ significantly between all PW and PW who were TgAb-negative. Conclusions: A median DBS-Tg of 10 g/L with <3% of values 44 g/L indicated population iodine sufficiency. Concurrent measurement of TgAb did not appear necessary to assess the population iodine status.

Thyroglobulin level at week 16 of pregnancy is superior to urinary iodine concentration in revealing preconceptual and first trimester iodine supply

“…Unlike in the ≥150 μg iodine/day group, the UIC of the <150 μg iodine/day group failed to reach iodine sufficiency (lower limit of sufficient median UIC in pregnancy by WHO definition is 150 μg/L). Serum Tg showed mild iodine deficiency (using cutoff value: 10 μg/L from Stinca et al, ) in both groups (Table ). The TSH concentrations were higher in the group with ≥150 μg/day iodine intake.…”

“…This can be avoided by excluding TgAb positive subjects. However, according to the data of others (Stinca et al, ; Vejbjerg et al, ) exclusion of TgAb positive cases did not alter their conclusions on the relationship between iodine nutrition and Tg in a population context. We screened the sera for TgAb and TgAb positive subjects were excluded.…”

“…The hCG concentration was a significant predictor for Tg in a group of iodine deficient pregnant women (Koukkou, Ilias, Mamalis, Adonakis, & Markou, ). Although recent data suggest that a median Tg below 10 μg/L (with less than 3% of individual values ≥44 μg/L) indicates iodine sufficiency in pregnant women using a dried blood spot Tg assay (Stinca et al, ), no accepted serum Tg reference range has been established for maternal iodine sufficiency.…”

Excess iodine intake: sources, assessment, and effects on thyroid function

“…Tg is a sensitive population indicator of both low and excess iodine intake, following a U‐shaped association with the UIC, as shown in schoolchildren (Fig. A), pregnant women, and infants . Elevated Tg normalizes in school‐age children after iodine repletion .…”

Risk of excessive intake of vitamins and minerals delivered through public health interventions: objectives, results, conclusions of the meeting, and the way forward

“…Iodine in urine is a strong biomarker because 90% is excreted within 24–48 h after consumption and measurement of iodine is relatively easy. Thyroglobulin is a sensitive biomarker of excessive iodine intakes and complements urinary iodine concentration for the evaluation of population iodine status, which should precede any review of salt iodization policy …”