The Medicare program was established in 1965 under Title XVIII of the Social Security Act. The program has become the principal means of providing health insurance coverage to the American population aged 65 and older as well as covering individuals with permanent disabilities or end-stage renal failure. Notwithstanding the enormous scale of the Medicare program, Congress has explicitly excluded a number of health care services. Section 1862(a)(1)(A) of Title XVIII states that the program may not pay for services that “are not reasonable and necessary for the diagnosis or treatment of illness or injury or to improve the functioning of a malformed body member.” Section 1862(a)(7) excludes routine physical examinations. These provisions have amounted to an exclusion of preventive services. In subsequent years Congress has overridden this exclusion for specific preventive services, adding them to the Medicare program.
Section 123 of the Consolidated Appropriations Act for 2001 commissioned the National Academy of Sciences, now known as the National Academies, “and as appropriate in conjunction with the United States Preventive Services Task Force, to conduct a study on the addition of coverage of routine thyroid screening using a thyroid stimulating hormone test as a preventive benefit provided to Medicare beneficiaries under Title XVIII of the Social Security Act for some or all Medicare beneficiaries” and to “consider the short-term and long-term benefits, and costs to the Medicare program, of such addition.” The serum thyroid stimulating hormone (TSH) assay is a common blood test that is already covered by the Medicare program for the diagnosis and treatment of illness. This volume, prepared by a committee appointed by the Institute of Medicine of the National
Academies, is an inquiry into the additional costs and benefits of also offering this test as a preventive service.
MEDICARE AND PREVENTIVE SERVICES
The initial focus of the Medicare program was to provide financial relief through substantial, if partial, reimbursement for the largest expenses of serious illness, particularly hospitalization. The original Medicare legislation excluded preventive services and routine physical examinations because they were not seen as part of the care of serious illness. These services were performed at the discretion of patients and doctors; their expense was foreseeable and not substantial.
Over time patterns of illness and treatment have changed. Illness is more commonly chronic and ongoing instead of acute and episodic. Most care is now provided outside the hospital. The Medicare program has adapted to most of these changes and covers most outpatient care. Coverage of preventive services (and prescription drugs) has been a significant exception. Individual preventive services have been added on an ad hoc basis through specific acts of Congress.
THYROID DYSFUNCTION AND ITS DIAGNOSIS
The thyroid gland produces and releases into the circulation hormones that influence basal metabolic processes in nearly all body tissues. Hypothyroidism, the lack of adequate production of thyroid hormones, can result in fatigue, lethargy, cold intolerance, slowed speech and intellectual function, slowed reflexes, hair loss, dry skin, weight gain, and constipation. Hyperthyroidism, the production of excessive amounts of thyroid hormones, can cause nervousness, anxiety, heart palpitations, rapid pulse, fatigability, tremor, muscle weakness, weight loss with increased appetite, heat intolerance, frequent bowel movements, increased perspiration, and often thyroid gland enlargement (goiter).
Thyroid gland function and hormone synthesis and release are regulated by thyroid stimulating hormone (TSH) that is secreted by the anterior pituitary gland. Inadequate thyroid gland output leads to high levels of TSH, while excessive thyroid hormone production suppresses production of TSH. Levels of serum TSH are generally the most sensitive indicator of thyroid gland function: Abnormal levels of TSH are often found even when serum levels of thyroxine, the principal hormone produced by the thyroid gland, are normal. By convention, abnormal levels of TSH in the presence of normal serum levels of free thyroxine are described as subclinical thyroid dysfunction; abnormal levels of TSH in the presence of abnormal serum levels of free thyroxine are described as overt thyroid dysfunction. This terminology can be confusing. Persons with “subclinical” thyroid dysfunction by this biochemical definition may display clear symptoms or signs of thyroid dysfunction while those with biochemically defined “overt” hypothyroidism may show no other evidence of thyroid dysfunction.
PREVALENCE AND CONSEQUENCES OF THYROID DYSFUNCTION
Thyroid dysfunction is common, especially in elderly people. Most people found to have abnormal serum levels of TSH in surveys have normal serum free thyroxine levels and are thus classified as having subclinical thyroid dysfunction, particularly subclinical hypothyroidism. Among people with subclinical thyroid dysfunction, most have very small increases or decreases in serum TSH concentrations. When asked, some of these people with subclinical thyroid dysfunction have symptoms that are compatible with, though not specific for, thyroid dysfunction, or have another indication for testing for thyroid dysfunction. Some people have biochemical or physiological abnormalities that are ameliorated by thyroid hormone therapy, in the case of people with subclinical hypothyroidism, or antithyroid therapy, in the case of subclinical hyperthyroidism. Among people with thyroid dysfunction, therapy may have beneficial effects on intermediate outcomes, such as reduction in serum lipid concentrations and improvement of myocardial contractility. However, appropriate therapy has not been proven to alter long-term morbidity or mortality in people with subclinical thyroid dysfunction. Similarly, while it is accepted that treatment will benefit patients with biochemically overt thyroid dysfunction who present with significant symptoms or complications, the lack of well designed studies makes it difficult to determine whether treatment would provide significant net benefit in persons who have biochemically defined overt thyroid dysfunction but little evidence of illness; the potential for harm is similar but potential for benefit is less. These uncertainties make it difficult to assess the value of a screening program for thyroid dysfunction.
SCREENING FOR THYROID DYSFUNCTION
Screening is the process of testing for a clinical condition when symptoms or other evidence of the presence of that condition either do not exist or, if present, are unrecognized by the health professional who orders the test. If a clinician suspects that clinically manifest thyroid dysfunction is present, TSH testing would not be considered screening; this is a diagnostic process that is already covered by Medicare. Under current coverage, a patient may be tested for thyroid dysfunction because of a broad range of symptoms associated with thyroid dysfunction; because thyroid dysfunction is a known cause or aggravating factor for many conditions such as atrial fibrillation, diabetes, hypertension, or hyperlipidemia; or because of a history of any kind of thyroid disease or exposure to an agent known to be thyrotoxic.
For a screening program to be successful, a number of important conditions must be satisfied. The natural history of the condition being screened must be understood so there is good evidence the disease outcome will be favorably influenced by further diagnosis and treatment. The screening test must be suit
ably reliable and valid so that most of those tested are accurately classified as to the current presence or absence of the disease in question. The screening test must be acceptable when applied to most persons for whom it is indicated. If not, the test will not effectively reach its intended target population and fail as a disease prevention measure. If a screening test indicates the possibility of a disease being present, there must be suitable, definitive tests to make a formal diagnosis of that condition. There must be proven, effective treatments for the conditions identified—treatments that lead to increased survival, function, or quality of life. Finally, there must be value to early intervention; diagnosis as a result of screening must provide a better chance of cure, less disability, a reduction in the development of pain or other significant symptoms, or enable treatment that is less arduous or expensive.
In the case of serum TSH screening for thyroid disease, these conditions are not fully satisfied. In its favor, the serum TSH test is reliable, valid, and acceptable to patients. The diagnosis of thyroid dysfunction can usually be made definitively. However, the natural history is not highly predictable; a large proportion of subjects screened who have positive test results will not develop significant morbidity from thyroid dysfunction. Available treatments can improve biochemical and physiological indications of thyroid dysfunction, but there are no studies of treatment of subjects identified through screening that show significant benefits from treatment in terms of improved survival, function, or quality of life. Treatment begun at the time of screening also has not been demonstrated to provide benefits greater than treatment initiated when the disease is clinically manifest.
THE COST OF COVERAGE
Estimates of the costs of screening require an estimate of the number of subjects who will be screened and the net costs incurred (or saved) as a result of screening.
Historically, the use of preventive services by Medicare beneficiaries has been considerably less than universal among those covered for the service; important factors have limited demand or created other barriers to use. In the case of serum TSH testing, more than 90 percent of Medicare beneficiaries have indications for testing that are already covered by the Medicare program. Aside from beneficiaries with known thyroid disease, fewer than 25 percent of beneficiaries with these indications are tested annually. On this basis, it is estimated that a relatively small number of Medicare beneficiaries would take advantage of a serum TSH screening benefit; our best estimate is 250,000 annually.
The Committee found a widespread lack of information necessary to make a meaningful assessment of the true economic costs of screening. It could not estimate costs avoided or other possible benefits resulting from screening or whether any costs incurred would be postponed rather than avoided if screening were not done. The Committee’s estimate of the cost of health care resources
likely to be expended for the initial screening test for 250,000 elderly beneficiaries was $5.9 million. The Medicare program would pay this entire amount. The Committee’s estimate of the lifetime cost of evaluating and treating those people with positive test results suggesting hypothyroidism was $24.7 million. The Medicare program would pay $11.6 million of this total; supplementary insurance or the beneficiaries themselves would pay the remaining $13 million. The Committee’s estimate of the lifetime cost of evaluating and treating those people with positive test results suggesting hyperthyroidism was $2.8 million. The Medicare program would pay $2.1 million of this total; supplementary insurance or the beneficiaries themselves would pay the remaining $0.6 million.
CONCLUSIONS AND RECOMMENDATIONS
The Committee reached two conclusions and makes a recommendation.
There is insufficient evidence to recommend periodic, routine screening for thyroid dysfunction among asymptomatic persons using serum TSH levels.
The basic reasons for this conclusion stemmed from several general considerations. It is uncertain whether asymptomatic persons with abnormal TSH levels actually have some degree of physiologically meaningful abnormalities that would benefit from early treatment in the absence of clinical manifestations. Some of the potentially important consequences of thyroid disease, such as altered blood cholesterol and lipid levels and bone density levels, are themselves the subject of recommended routine clinical screening procedures; these should be performed as part of a general program of preventive care regardless of a potential relation to possible thyroid dysfunction. While some individuals with unrecognized clinical or physiological abnormalities associated with thyroid dysfunction do progress to more severe thyroid disease over several years, the rates, timing, and risk factors for this progression are only partly understood. Finally, routine TSH screening of asymptomatic persons over 65 years of age may lead to large numbers of persons receiving thyroid hormone therapy, but no randomized clinical trials have been performed that assess the long-term benefits or adverse effects of early treatment of thyroid dysfunction.
Given insufficient evidence about the health benefits of a serum TSH screening program, the net cost implications for the Medicare program are uncertain.
Because evidence is lacking on the likely health benefits of screening, there is no reasonable basis for estimating whether a screening program would detect thyroid dysfunction more effectively than usual care and hence how the costs of treating thyroid dysfunction under these alternative strategies would compare. We do not have an adequate basis for estimating whether there would be any net
savings or additional costs associated with treating future consequences of thyroid dysfunction.
The Medicare program at this time should not cover screening for thyroid dysfunction as a preventive services benefit. This recommenda tion is based on the lack of sufficient evidence of either net benefit or harm. Additional evidence is required for a definitive conclusion.