Serum and Dried Blood Spot Thyroglobulin as a Functional Biomarker of Iodine Status during Pregnancy

Abstract

Objectives: Thyroglobulin (Tg) is a sensitive marker for iodine deficiency and excess in school-aged children. DBS-Tg may be a promising functional biomarker also during pregnancy. Our objectives were to develop a new Tg assay and to determine if trimester-specific reference ranges are needed. Methods: A new Tg-ELISA for serum and DBS was developed, tested, and validated against Immulite, a conventionally serum Tg assay. Subjects were healthy women in 1st, 2nd and 3rd trimester of pregnancy. Serum or DBS-Tg concentrations were compared from iodine sufficient women in India (n=160) and Switzerland (n=590) to mildy iodine-deficient women in Thailand (n=260).  Results: Median (IQR) serum Tg (µg/L) in mildly iodine-deficient Thai pregnant women with a median baseline UIC (IQR) of 110 (69-172) µg/L were: 9.6 (6.4-17.0), 10.4 (5.6-15.9), 11.9 (6.4-22.3) in the 1st, 2nd and 3rd trimesters, respectively. Median (IQR) serum Tg (µg/L) in iodine sufficient Indian pregnant women with a median baseline UIC (IQR) of 184 (97-349) µg/L were: 7.1 (2.9-12.4), 7.2 (3.7-11.5), 7.0 (4.0-11.4) in the 1st, 2nd and 3rd trimesters, respectively. Median (IQR) DBS-Tg (µg/L) in iodine sufficient Swiss pregnant women with a median baseline UIC (IQR) of 162 (83-284) µg/L were: 7.9 (3.4-12.8) and 9.0 (4.3-15.8) in the 2nd and 3rd trimesters, respectively. Conclusions: Serum Tg concentrations may be higher in mildly iodine-deficient women compared to iodine sufficient women, and in iodine sufficient women, DBS-Tg concentrations may be higher than serum Tg concentrations. These data will contribute to the development of reference ranges for Tg concentrations to define iodine sufficiency in pregnant women.