What are the causes of elevated TSH in a newborn?

Maternal thyroid disease can also cause a suppression of thyroid function in the newborn. One study¹ found that of 34 children with transient hypothyroidism, 10 had mothers with undertreated or unrecognized Graves disease.

Finally, either iodine excess or iodine deficiency can cause transient hypothyroidism. Case reports have directly demonstrated the effects of topical iodine exposure on newborn TSH levels.^3-5 Deficiency of dietary iodine is a common cause of both congenital and transient hypothyroidism in newborns worldwide, although it is rare in the United States. The World Health Organization lists 54 countries with inadequate iodine intake; consider children from these countries at high risk for hypothyroidism due to iodine deficiency.⁶

Draw TSH on the second or third day of life

In term, healthy newborns, TSH levels normally increase to levels of 60 mU/L within 30 minutes of delivery. This is followed by a rapid decline in TSH levels over the first 5 days of life to <10 mU/L. An Australian study found more elevated TSH levels for samples drawn on day 2 of life compared with day 3 of life, likely reflecting normal postnatal physiology.³ Age-specific reference ranges are necessary for interpretation of TSH levels during the first 5 days of life. The second or third day of life remains the optimal time for screening when appropriate reference ranges are used.

Recommendations from others

The United States Preventive Services Task Force (USPSTF),⁷ the American Academy of Family Physicians,⁸ the American Academy of Pediatrics,⁹ and the American Thyroid Association (ATA)¹⁰ all recommend routine screening of asymptomatic newborns for congenital hypothyroidism. The USPSTF recommends that clinicians evaluate abnormal thyroid screening results with a supplemental lab test, using TSH as the primary test and T4 as the supplemental test.⁷ Additionally, the ATA endorses a second thyroid screening at 7 to 14 days of life to increase specificity of congenital hypothyroidism screening.¹⁰