The scenario is fairly common: you are in your medical provider’s office for a checkup and also happen to be getting lab work done. You report that you have no symptoms of feeling cold or fatigue, denying weight gain or weight loss, and do not have palpitations or dizziness. Should your medical provider order blood work to evaluate the function of your thyroid gland, commonly known as TSH or thyroid stimulating hormone or T4, another component integral to thyroid function?
Well, according to the most recent report of the United States Preventive Services Task Force (USPSTF), a group of medical experts advising the government, the answer is not clear, as more clinical trials and scientific evidence will be necessary to ultimately make a better decision.
In doing so, the USPSTF reverted back to its most recent recommendation, issued in 2004, which advised against routine screening for thyroid disease in persons who are not pregnant, and otherwise healthy and asymptomatic, without significant risk factors for hyperthyroidism or hypothyroidism.
As stated in today’s report:
“The Task Force concludes that current evidence is insufficient to assess the balance of benefits and harms of screening for thyroid dysfunction in nonpregnant, asymptomatic adults.”
In doing so, the USPSTF also warned against the potential risks for screening asymptomatic individuals, including falsely positive results which could result in potential physical harms from overtreatment as well as psychological effects from labeling persons with a specific condition or disease.
However, it is important to note is that these updated recommendations do not apply to those persons who have symptoms such as weight gain, weight loss, palpitations, fatigue, or skin changes.
For those with symptoms and laboratory-confirmed hypothyroidism, levothyroxine can be prescribed by a medical provider to alleviate symptoms. In fact, in 2011, based on data from the USPTF’s report, nearly 71 million people received a prescription for this medication.
The report continues:
“The USPSTF concludes that the evidence is insufficient and that the balance of benefits and harms of screening for thyroid dysfunction in nonpregnant, asymptomatic adults cannot be determined.
If clinicians offer screening for thyroid dysfunction to asymptomatic persons, they should first ensure that patients clearly understand the uncertainties surrounding any potential clinical benefit of screening as well as the possibility of harm this choice may engender.”
The thyroid gland, located in the front of the neck surrounding the voice box or larynx, produces important hormones which are integral to metabolism and growth, and abnormal levels can be linked to cancer and heart disease as well as death if not treated.
Disorders of the thyroid gland are among the most common conditions of the endocrine glands treated by medical providers, ranging from asymptomatic to mild disease states which can encompass asymptomatic as well as overt states of hypothyroidism or hyperthyroidism. In rare cases, potentially life-threatening complications can develop such as thyroid storm, related to untreated hyperthyroidism, or so called myxedema coma related to severe hypothyroidism.
A simple blood test for thyroid stimulating hormone, commonly referred to as TSH, is the first step in screening persons for thyroid disease, along with T4 as well as T3, other aspects of what we refer to as a thyroid profile.
Arguments To Screen According To USPSTF
The argument for early detection and treatment of asymptomatic persons (with abnormal levels of TSH) is to treat the potential complications of unrecognized disease such as cardiac complications including atherosclerotic heart disease, and resulting heart failure related to hyperthyroid states, along with potential fractures related to abnormal bone metabolism associated with hypothyroidism. The underlying risk of cancer remains another argument to embark on screening asymptomatic persons.
The flip side of the argument to screen, endorsed by USPSTF, is that such widespread screening practices, especially in cases of what we refer to as subclinical thyroid dysfunction–patients with abnormal levels of TSH but no overt symptoms–may lead to not only false positive results, but overtreatment and other emotional harms due to labeling those with a disease.
The USPSTF, however, does concede that screening can reliably detect “abnormal” TSH levels in persons without overt symptoms. That said, it should be noted there is no broad agreement by laboratories or even medical providers as to what reference ranges and values actually constitute an abnormal TSH level, referring to “cutoff points for the lower and upper boundaries of normal TSH levels in the general population and in subgroups, such as older adults.”
The Black Box Of TSH Screening
It turns out that generalized laboratory reference intervals currently in use are actually based on the statistical distribution of TSH levels across the general population rather than the correlation of a specific TSH level with symptoms, risk factors, or adverse clinical outcomes for disease.
As a result, the lack of clearly delineated reference levels may lead to confusion among patients who need validation for the risks of having a particular thyroid condition based on their levels of T4 and TSH.
Other medical conditions sensitive to TSH secretion can also impact results and cloud accurate interpretation of serum TSH levels, leading to inconsistent and variable results during testing.
As a result of these uncertainties, many professional societies recommend repeating thyroid function tests if the results are inconsistent at 3 to 6 month intervals in asymptomatic persons before making a diagnosis or planning specific treatment–unless the serum TSH level is greater than 10.0 or less than 0.1.
Health Benefits To Screening?
Overall, the USPSTF did not find evidence that screening for abnormal thyroid lab values reduces cardiovascular disease, complications or associated death, in healthy persons with no risk factors or family history to suggest abnormal thyroid function. It also found that screening healthy, asymptomatic adults “does not improve quality of life or provide clinically meaningful improvements in blood pressure, body mass index (BMI), bone mineral density, or lipid levels. It also does not improve cognitive function.”
Preventable Disease Screening
In the US, nearly 3% of men and 5% of women have subclinical hypothyroidism. However based on multiple studies, about 37% of patients actually normalize their lab values over several years time without any intervention. Only 2-5% of patients with subclinical hypothyroidism go on to actually develop symptoms or “overt thyroid dysfunction.”
In fact, a previous retrospective cohort study noted that those persons with subclinical hypothyroidism who took T4 had a lower risk for ischemic heart disease events and overall mortality. Unfortunately, the USPSTF was not able to pinpoint any prospective studies examining the relationship between treatment and risk for cardiac events.
Subclinical hyperthyroidism occurs in nearly 0.7% of persons in the US, more often in women than men. About 25 % of persons with subclinical hyperthyroidism will actually normalize their TSH without any medical intervention within 2 years. And close to 1% to 2% of persons with TSH levels less than 0.1 mIU/L develop “overt” hyperthyroidism (with or without symptoms). Overall, persons with TSH levels between 0.1 and 0.45 mIU/L generally do not go on to develop “overt” hyperthyroidism.
Potential Harms With Screening
As mentioned previously, the most important potential harms are false-positive results, labeling of patients with a specific disease, as well as overdiagnosis and overtreatment.
Its clear that false positive results may occur primarily due to the variable nature of TSH secretion often times the result of illness or particular medications. The lack of consensus on what constitutes a normal reference interval also makes treatment problematic.
Furthermore, agreement is not clear regarding the actual threshold when clinicians should begin medication, especially for hypothyroidism. There has not been any clear data from clinical trials to identify a numeric point to begin medication that can to improve clinical outcomes. Clinical consensus has been that a TSH level greater than 10.0 mIU/L is generally considered the threshold for initiation of treatment mainly due to risk of developing overt hypothyroidism. For those patients with a TSH between and 4.5 -10.0, the decision to begin treatment is controversial, and should be based on serial TSH levels, as well as development or progression of any symptoms.
Endocrine Specialty Groups Recommend Thyroid Screening: The Alternate View
The USPSTF, while endorsing evidence-based recommendations that are typically designed to treat large populations, realizes that the major endocrine specialty societies continue to recommend screening for thyroid dysfunction.
As an example, The American Thyroid Association (ATA) endorses screening in all nonpregnant adults beginning at age 35, and subsequently every 5 years.
In reality, the majority of practicing endocrinologists, including the American Association of Clinical Endocrinologists (AACE) recommends routine TSH screening in older female patients with nonspecific symptoms. And as mentioned, the bulk of the USPSTF recommendations are often based on evaluation of large populations of patients, as opposed to individual patient situations, and thus generally conservative in nature.
The USPSTF’s recommendations often point to the lack of randomized prospective trials showing benefits of treatment in mild hypo- or hyperthyroidism, typically related to treating large populations, while also addressing costs.
Meanwhile, the majority of practicing endocrinologists focus on individual assessment of patients, generally opting to treat mildly symptomatic patients with hypo- or hyperthyroidism to achieve potentially mild, but often significant benefits.