Controversies on Screening and Treatment of Hypothyroidism—Commentary
January is Thyroid Awareness Month, and is thus a good time to remind practitioners that about 1 in 8 Americans will develop a thyroid condition during their lifetime. However, according to the American Thyroid Association (ATA), approximately 60 percent of these individuals are unaware of their condition. Although many with thyroid conditions are undiagnosed, debates continue around the optimal strategies to detect and treat hypothyroidism.
There is no debate that patients with symptoms or signs suggestive of hypothyroidism should be tested for thyroid dysfunction by measurement of thyroid stimulating hormone (TSH) and free thyroxine (T4) levels. However, recommendations for screening (ie, testing of asymptomatic patients) for this disorder vary.
The U.S. Preventive Services Task Force (USPSTF) has found insufficient evidence to justify regular screenings for thyroid dysfunction in nonpregnant, asymptomatic adults. However, the USPSTF guidelines differ from those of endocrine societies, including the American Thyroid Association (ATA). The ATA recommends screening adults for thyroid dysfunction by measurement of the TSH level beginning at age 35 and every five years thereafter. The American Academy of Family Physicians recommends screening people beginning at age 60. Most endocrinologists favor regular thyroid screenings every five years for women beginning at age 35 and men beginning at age 65. Once patients reach age 70, more frequent screenings can be beneficial.
Rationale in favor of such testing includes one recent study that found nearly 6 percent of overtly hypothyroid patients showed no symptoms and about 8 percent had only one symptom, indicating that testing only patients with typical symptoms would miss a portion of the population with hypothyroidism.
It’s important to reiterate that this recommendation is only for asymptomatic patients; patients displaying symptoms of hypothyroidism should have TSH levels measured regardless of age.
There is little debate about screening for hypothyroidism in newborns, which is mandatory in much of the developed world. Congenital hypothyroidism occurs at a rate of about 1 in 3,000 newborns. Unfortunately, much of the developing world has not implemented universal screening.
Screening pregnant women or women who desire pregnancy is another area of controversy. Some physicians recommend screening all women who desire pregnancy or who are pregnant. Professional societies such as the ATA and American College of Obstetricians and Gynecologists recommend targeted screenings for pregnant women. This may include pregnant women who:
- Display symptoms of thyroid dysfunction
- Come from an area where moderate to severe iodine insufficiency occurs
- Have a family or personal history of thyroid disorders
- Have type 1 diabetes
- Have a history of infertility, preterm delivery, or miscarriage
- Have had head or neck radiation therapy
- Are morbidly obese (BMI > 40 kg/m2)
- Are older than 30
In addition to screening for hypothyroidism with TSH, other laboratory tests may be a clue to an underactive thyroid gland. Results indicating unexplained hyponatremia, a high creatine phosphokinase, or elevated prolactin level may be indicative of thyroid dysfunction. Additionally, high triglycerides (TGs) and high low-density lipoprotein (LDL) levels could also indicate a thyroid problem.
Treatment of Hypothyroidism
Treatment for hypothyroidism generally consists of starting levothyroxine (T4) at low doses and titrating up every few weeks until the TSH normalizes.
However, approximately 15 percent of patients treated with only levothyroxine don’t feel as well as they did prior to developing hypothyroidism. In these patients, one option is to add triiodothyronine (T3), which can be synthetic T3 or desiccated thyroid extract from porcine or bovine thyroid glands. The ATA and the American Association for Clinical Endocrinology (AACE) disagree over adding T3. The ATA’s latest guidelines do not rule out the use of T3 in some cases, and the AACE has not endorsed these guidelines, noting they may lead to increased T3 testing and unwarranted treatment. Although clinical experience indicates that T3 is occasionally helpful, a majority of studies fail to demonstrate benefit. Thus, substituting some T3 for a portion of the T4 therapy may be performed as a clinical trial in a specific patient, but the serum TSH needs to be maintained in the normal range on the combined therapy.
Physicians can refer patients to the Manuals consumer pages on an overview of the thyroid gland and hypothyroidism for more resources.