Question

An 8-day old newborn was found to have a thyroid – stimulating hormone level of more than 100 mIU/L. Which of the following will be the next best investigation?

• A. Urine iodine excretion
• B. Serum thyroid receptor antibody
• C. Radiotracer uptake with technetium
• D. Perchlorate secretion

Answer 1

The Correct Option is C

An 8-day old newborn with a thyroid-stimulating hormone (TSH) level exceeding 100 mIU/L suggests congenital hypothyroidism. To further investigate and confirm the diagnosis, we should assess thyroid function and anatomy through imaging. The high TSH level indicates the need to evaluate the thyroid gland's ability to capture iodine, which is critical for thyroid hormone synthesis. Among the options provided:

Urine iodine excretion

Serum thyroid receptor antibody

Radiotracer uptake with technetium

Perchlorate secretion

The most relevant and informative investigation is:

• Radiotracer uptake with technetium: This test evaluates the thyroid gland's ability to uptake iodine or a similar tracer, such as technetium. It helps to confirm the presence and functional capacity of thyroid tissue. A lack of uptake can indicate an absent or ectopic thyroid gland or dyshormonogenesis (a defect in hormone synthesis).

Other options are less useful in this context:

• Urine iodine excretion: Useful for assessing iodine deficiency but not directly helpful in diagnosing congenital hypothyroidism.
• Serum thyroid receptor antibody: Indicated in immune-mediated thyroid disorders, not typically in newborns.
• Perchlorate secretion: A specialized test for diagnosing certain types of dyshormonogenesis but not the first-line test.

Thus, radiotracer uptake with technetium is the next best investigation to determine the cause of congenital hypothyroidism in this newborn.